IVRS

VOICE INTERACTIVE SYSTEM FOR COLLEGE

AUTOMATION

Now-a-days every ins t i tu t ion needs automat ion. As a

par t of col lege automat ion, we have decided to do a projec t

“Voice In terac t ive System for Col lege Automat ion” . Our

projec t a l lows the user to know the s tudent ’s a t tendance and

marks quickly through the te lephone l ine wi thout the

in tent ion of the col lege author i ty . In the hardware s ide

embedded sys tem has been used. A 20 pin microcontro l le r

89C2051 is used because of i t s compat ib i l i ty wi th our

hardware . This microcontro l le r cont ro ls the whole hardware .

Telephone l ine i s used for communica t ion purpose . Visual

Bas ic has been used for sof tware programming. Presenta t ion

in the c lass and outcome of the univers i ty are made reachable

to the parents by our projec t . I t wi l l be very obl ig ing to the

parents to be acquainted wi th the i r son’s /daughter ’s rec i ta l in

the col lege .

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1 . INTRODUCTION

Embedded sys t em i s a sy s t em i s a sy s t em tha t l i ve s i n s ide

ano the r dev i ce and ac t a s a ha rdware componen t o f t ha t dev i ce . An

embedded sys t em can be de s i r ab l e once cons i s t i ng o f a p roce s so r ,

a s soc i a t ed pe r i phe ra l s and so f twa re u sed fo r a spec i f i c pu rpose . The

embedded sys t em de f ined a s t he s e t o f ha rdware con t ro l l ed by

so f twa re . L ike any compu t ing sy s t em an embedded sys t em i s a

combina t i on o f so f twa re and ha rdware .

In ou r P ro j ec t a 20 p in Mic rocon t ro l l e r AT89C2051 i s u sed t o

con t ro l t he who le ha rdware . The Mic rocon t ro l l e r s ense s t he DTMF

s igna l t h rough t he DTMF decode r IC MT8870 and i t r e sponds

acco rd ing t o t he decoded s i gna l . The c i r cu i t ha s an i nbu i l t Phone R ing

s enso r c i r cu i t and t he sy s t em wi l l t ake ove r t he phone au toma t i ca l l y

u s ing a 12 V r e l ay . The mic rocon t ro l l e r w i l l r e ce ive t he s i gna l f r om

the d i s t ance t e l ephone and i t decodes t he s i gna l and f e t che s t he da t a

f rom the PC th rough t he s e r i a l po r t , ba sed on t he t e l ephone s i gna l ,

and s ends t he da t a t h rough t he t e l ephone l i ne .

The ob j ec t i ve o f ou r p ro j ec t i s t o know the s t uden t ’ s a t t endance

and marks qu i ck ly t h rough t he t e l ephone w i thou t t he i n t en t i on o f t he

co l l ege au tho r i t y . By d i a l i ng t he p rov ided t e l ephone number , one can

ab l e t o d ig up t he i n fo rma t ion o f t he s t uden t . One o f t he advan t ages i s

t he t ime spend ing fo r co l l ege o f f i c i a l s i n a t t emp t ing phone ca l l s f r om

ou t s i de r s w i l l be r educed .

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2 . PROJECT DESCRIPTION

2.1 . BLOCK DIAGRAM

Figu re 2 .1 Bas i c B lock D iag ram

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2 .2 BLOCK DIAGRAM EXPLANATION

The above B lock d i ag ram cons i s t o f f o l l owing B locks

1 . Te l ephone s ec t i on

2 . DTMF Decode r

3 . R ing De t ec to r

4 . ON/OFF hook S imu la to r

5 . Mic rocon t ro l l e r

6 . Vo l t age conve r t e r

7 . PC Se r i a l Po r t

8 . Pe r sona l Compu te r (PC)

1 . TELEPHONE

Inven t ed by Be l l and h i s a s s i s t an t , Thomas A . Wa t son , t he

t e l ephone marked a s i gn i f i c an t deve lopmen t i n t he h i s t o ry o f

e l e c t r i c a l commun ica t i on sy s t ems . I n t he e a r l i e s t magne to - t e l ephone

o f 1876 , t he speake r ’ s vo i ce was conve r t ed i n to e l e c t r i c a l ene rgy

pa t t e rn s t ha t cou ld be s end ove r r e a sonab ly l ong d i s t ance s ove r w i r e s

t o a r e ce ive r , wh i ch wou ld conve r t t he se ene rgy pa t t e rn s back i n to t he

o r i g ina l sound waves fo r t he l i s t ene r .

Outgo ing Ca l l

The d i a l pad , a l so ca l l ed keypad o r t ouch - tone pad , i s u sed t o

d i a l t e l ephone number s a s we l l a s i n t e r ac t w i th vo i ce p roce s s ing

sy s t em such a s a vo i ce ma i l and i n t e r ac t i ve vo i ce r e sponse ( IVR) . The

add re s s s i gna l i ng fo r an ou tgo ing ca l l c an be accompl i shed by 3

d i f f e r en t me thods : pu l s e d i a l ( r o t a ry ) , r e a l t one mu l t i p l e f r equency

(DTMF) , o r mu l t i f r equency (MF)

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Mult i -Frequency (MF) :

I t howeve r became more popu l a r w i th t he i n t roduc t i on o f dua l

t one mu l t i p l e f r equency (DTMF) mode o f d i a l i ng . S ing l e ch ip DTMF

encode r s /decode r s a r e ava i l ab l e t oday , wh ich make t he de s ign ing such

sy s t ems ea sy and r e l i ab l e

Mul t i - f r equency s i gna l i ng i s s im i l a r t o DTMF and i s u sed on

t r unk c i r cu i t , p ay t e l ephones . Combina t i on o f two t ones i s u sed t o

t r ansmi t s i gna l i ng i n fo rma t ion , MF and DTMF s igna l s a r e more

r e l i ab l e and cons ide rab ly f a s t e r t han pu l s e d i a l . I n bo th me thods ,

d ig i t s a r e t r ansmi t t ed a t t he r a t e o f abou t 7 d ig i t s pe r s econd .

Tone combinat ion Dig i t

700+900 1

700+1100 2

900+1100 3

700+1300 4

900+1300 5

1100+1300 6

700+1500 7

900+1500 8

1100+1500 9

1300+1500 0

Tab le .2 .1 . Mu l t i p l e F requency fo r Number s

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Incoming ca l l

When a t e l ephone s e t i s c a l l ed , t he l oca l exchange gene ra t e s a

h igh r i ng vo l t age o f abou t 90 -105Vol t s AC wi th a f r equency o f 20Hz

supe r imposed ove r t he minus ( - ) 48Vo l t DC. A capac i t o r i n t he phone

pa s se s t he AC bu t b lock DC. Upon de t ec t i ng t he AC vo l t age , t he

phone p rov ide s an aud ib l e s i gna l t ha t a l t o s t he u se r o f an i ncoming

ca l l . Each t e l ephone s e t p rov ide a r i nge r equ iva l en t numbe r (REN) a s

de f i ned w i th in FCC pa r t 68 and E IA RS-470 .The REN i s u sed t o

ensu re t ha t t he l oca l exchange can p rov ide t he co r r ec t amoun t o f

power r equ i r ed t o r i ng t he t e l ephone . I t de sc r i be s t he f r equency

r ange , power r ange , and b i a s vo l t age r ange o f t he t e l ephone s e t . When

t he phone i s an swered , DC cu r r en t beg in s t o f l ow in t he l oop . The

l oca l exchange t he cu r r en t f l ow and r emoves t he supe r imposed r i ng

vo l t age . The -48Vo l t s DC tha t i s a lways on t he l i ne ope ra t e s t he

t e l ephone when i t i s be ing u sed .

2 DTMF SIGNALING

DTMF s t ands fo r Dua l Tone Mul t i p l e F requency . I t i s a

t one cons i s t i ng o f two f r equenc i e s supe r imposed . I nd iv idua l

f r equenc i e s a r e chosen such t ha t i t i s e a sy t o de s ign f i l t e r s and ea sy

t o t r ansmi t t he t ones t h rough a t e l ephone l i ne hav ing bandwid th o f

app rox ima te ly 3 .5 kHz . DTMF was no t i n t ended t o be u sed fo r da t a

t r ans f e r , i t was mean t t o be u sed fo r s end ing t he con t ro l s i gna l s a l ong

t he t e l ephone l i ne . Wi th s t anda rd decode r s i t i s pos s ib l e t o s end 10

beeps pe r s econd i . e . , f i ve b i t s pe r s econd . DTMF s t anda rd spec i f i e s

50ms t ones and 600ms du ra t i on be tween two succe s s ive t ones .

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Tab l e .2 .2 . DTMF Keypad F requenc i e s

Theory o f Opera t ion

In DTMF the re a r e 16 d i s t i nc t t ones . Each t one i s t he sum o f

two f r equenc i e s : one f rom a l ow and one f rom a h igh f r equency g roup .

The re a r e fou r d i f f e r en t f r equenc i e s i n e ach g roup . Our phone on ly

u se s 12 o f t he pos s ib l e 16 t ones . I f you l ook a t you r phone , t he r e a r e

on ly 4 rows (R1 , R2 , R3 and R4) and 3 co lumns (C1 , C2 and C3) . The

rows and co lumns s e l ec t f r equenc i e s f rom the l ow and h igh f r equency

g roup r e spec t i ve ly .

The fo l l owing g r aph i s a c ap tu r ed s c r een f rom an o sc i l l o scope .

I t i s a p lo t o f t he t one f r equency fo r t he "1" key :

1209 Hz 1336 Hz 1477 Hz 1633 Hz

697 Hz 1 2 3 A

770 Hz 4 5 6 B

852 Hz 7 8 9 C

941 Hz * 0 # D

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Figure 2.2 Tone frequencies for key “1”

You can s ee t ha t t he DTMF gene ra t ed s i gna l i s ve ry d i s t i nc t and

c l ea r . The ho r i zon t a l ax i s i s i n s amp le s . The f r equency o f t he t one i s

abou t 1900 Hz - c l o se t o t he 1906 Hz p red i c t ed by Tab l e 3

(697+1209) .

No t e t ha t t he l a s t co lumn i s no t common ly s een i n t he

t e l ephones t ha t we u sed , bu t t e l ephone exchanges u se t hem qu i t e

o f t en . Nowadays , DTMF i s u sed fo r d i a l i ng t he number s i n

t e l ephones , con f igu r ing t e l ephone exchanges e t c . A CB t r ansce ive r o f

2 .7 MHz i s no rma l ly u sed t o s end f l oa t i ng codes . DTMF was de s igned

t o be ab l e t o s end t he codes u s ing mic rophone . Each beep (o r d ig i t

you d i a l on t he t e l ephone ) i s composed o f two concu r r en t f r equenc i e s ,

wh i ch a r e supe r imposed on amp l i t ude . The h ighe r o f t he two

f r equenc i e s i s no rma l ly a l oud by 4dB , and t h i s sh i f t i s t e rmed a s

tw i s t . I f t he tw i s t i s equa l t o 4dB , t he h ighe r f r equency i s l oud by

4dB . I f t he l ower f r equency i s l oud , t hen t he tw i s t i s s a id t o be

nega t i ve .

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Event Low frequency High frequency

Busy signal 480 Hz 620 Hz

Dial tone 350 Hz 440 Hz

Ringback tone (US) 440 Hz 480 Hz

Tab l e .2 .3 . DTMF Even t F requenc i e s

The t one f r equenc i e s , a s de f i ned by t he P rec i s e Tone P l an , a r e

s e l ec t ed such t ha t ha rmon ic s and i n t e rmodu la t i on p roduc t s w i l l no t

c ause an un re l i ab l e s i gna l . No f r equency i s a mu l t i p l e o f ano the r , t he

d i f f e r ence be tween any two f r equenc i e s does no t equa l any o f t he

f r equenc i e s , and t he sum o f any two f r equenc i e s does no t equa l any o f

t he f r equenc i e s . The f r equenc i e s we re i n i t i a l l y de s igned w i th a r a t i o

o f 21 /19 , wh ich i s s l i gh t l y l e s s t han a who le t one . The f r equenc i e s

may no t va ry more t han ±1 .5% f rom the i r nomina l f r equency , o r t he

sw i t ch ing cen t e r w i l l i gno re t he s i gna l . The h igh f r equenc i e s may be

t he s ame vo lume o r l oude r a s t he l ow f r equenc i e s when s en t a c ro s s

t he l i ne . The l oudnes s d i f f e r ence be tween t he h igh and l ow

f r equenc i e s c an be a s l a rge a s 3 dec ibe l s ( dB) and i s r e f e r r ed t o a s

" tw i s t " .

Genera t ing DTMF

DTMF s igna l s c an be gene ra t ed t h rough ded i ca t ed ICs o r by u s ing

RC ne tworks connec t ed t o a m ic rop roces so r . MT8880 i s an example o f

a ded i ca t ed IC . Bu t ge t t i ng t he l a t t e r me thod work i s a b i t d i f f i cu l t i f

h i gh accu racy i s needed . The c ry s t a l f r equency needs t o be s ac r i f i c ed

fo r a non s t anda rd cyc l e l eng th . Hence t h i s me thod i s u sed fo r s imp le

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app l i c a t i ons . Mos t o f t en , a P IC mic ro cou ld be u sed fo r t he above

pu rpose .

Decod ing DTMF

Detec t i ng DTMF wi th s a t i s f ac to ry p r ec i s i on i s a ha rd t h ing .

Of t en , a ded i ca t ed IC such a s MT8870 i s u sed fo r t h i s pu rpose . I t u se s

two 6 th o rde r band -pas s f i l t e r s u s ing sw i t ched capac i t o r f i l t e r s and i t

supp re s se s any ha rmon ic s . Hence t hey can p roduce p r e t t y good s i ne

waves f rom d i s t o r t ed i npu t . Hence i t i s p r e f e r r ed . Aga in

mic rop roces so r s c an a l so be u sed , bu t t he i r app l i c a t i on i s l im i t ed .

3 . RING DETECTOR:

I t i s u sed t o de t ec t t he r i ng s i gna l f r om the t e l ephone l i ne . I t

g i ve s ou t a l og i ca l ou tpu t t o t he mic rocon t ro l l e r . An op tocoup l e r

MCT2E i s u sed a s r i ng de t ec to r .

I f r i ng i s p r e sen t – log i c 0

E l s e - l og i c 1

Norma l t ime vo l t age i n t e l ephone l i ne=48V d . c

OFF hook vo l t age -12V d . c

R ing s i gna l vo l t age -75V a . c

4 . ON–OFF HOOK SIMULATOR

I t i s u sed t o p i ckup t he t e l ephone e l ec t ron i ca l l y . A 12 vo l t d . c

s i gna l i s ob t a ined by p l ac ing a r e s i s t o r a c ro s s t he t e l ephone l i ne . I t i s

u sed t o de t ec t whe the r t he Hand s e t i s i n ON hook cond i t i on o r OFF

hook cond i t i on so a s t o s end t he i n fo rma t ion t o t he mic rocon t ro l l e r . A

12 V r e l ay i s u sed fo r t he pu rpose .

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5 . MICROCONTROLLER

A by-p roduc t o f m ic rop roces so r deve lopmen t was t he

mic rocon t ro l l e r . The s ame f ab r i c a t i on t e chn iques and p rog ramming

concep t s t ha t make pos s ib l e t he gene ra l -pu rpose mic rop roces so r a l so

y i e lded t he mic rocon t ro l l e r .

Mic ro con t ro l l e r s a r e no t a s we l l known to t he gene ra l pub l i c ,

o r t o many i n t he t e chn i ca l commun i ty , a s a r e t he more g l amorous

mic rop roces so r . The pub l i c i s , howeve r , ve ry we l l awa re t ha t

“ some th ing” i s r e spons ib l e fo r a l l o f t he smar t VCRs , c l ock r ad io s ,

washe r s and d rye r s , v ideo games , t e l ephones , m ic rowaves , TVs ,

au tomob i l e s , t oys , vend ing mach ine s , cop i e r s , e l eva to r s , i r ons , and a

myr i ad o f o the r a r t i c l e s t ha t a r e i n t e l l i gen t and “p rog rammab le” .

Compan i e s a r e a l so awa re t ha t be ing compe t i t i ve i n t h i s age o f t he

m ic roch ip r equ i r e s t he i r p roduc t s , o r t he mach ine ry t hey u se t o make

t hose p roduc t s , t o have some “ smar t s ” .

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Microproces sor and Microcontro l l e r

Mic rop roces so r and mic rocon t ro l l e r s t em f rom the ba s i c i dea ,

a r e made by t he s ame peop l e , and a r e so ld t he s ame t ype o f sy s t em

des igne r s and sy s t em p rog rammers . Wha t i s t he d i f f e r ence be tween

t he two?

Microproces sor

A mic rop roces so r , a s t he t e rm has come t o be known , i s a

gene ra l -pu rpose d ig i t a l compu te r c en t r a l p roce s s ing un i t (CPU) .

A l though popu l a r l y known a s a “ compu te r on a ch ip” , t he

m ic rop roces so r i s i n no s ense a comple t e d ig i t a l compu te r .

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Figu re . 2 . 3 B lock D iag ram o f a Mic rop roces so r

Thi s b lock d i ag ram con t a in s a r i t hme t i c and l og i c un i t (ALU) , a

p rog ram coun t e r (PC) , a s t a ck po in t e r (SP) , some work ing r eg i s t e r s , a

c l ock t im ing c i r cu i t , and i n t e r rup t c i r cu i t s . To make a comple t e

m ic rocompu te r , one mus t add memory , u sua l l y r e ad -on ly p rog ram

memory (ROM) and r andom-acces s da t a memory (RAM) , memory

decode r s , an o sc i l l a t o r , and a number o f i npu t / ou tpu t ( I /O) dev i ce s ,

such a s i n t e r rup t hand l e r s and coun t e r s , may be added t o r e l i eve t he

CPU f rom t ime consuming coun t i ng o r t im ing cho re s . Equ ipp ing t he

mic rocompu te r w i th mass s t o r age dev i ce s , common ly a f l oppy and

ha rd d i sk d r i ve s , and I /O pe r i phe ra l s , such a s keyboa rd and a CRT

d i sp l ay , y i e ld s a sma l l compu te r t ha t c an be app l i ed t o a r ange o f

gene ra l -pu rpose so f twa re app l i c a t i ons .

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The ha rdware de s ign o f a m ic rop roces so r CPU i s a r r anged so

t ha t a sma l l o r ve ry l a rge sy s t em can be con f igu red a round t he CPU a s

t he app l i c a t i on demands . The p r ime u se o f a m ic rop roces so r i s t o r e ad

da t a , pe r fo rm ex t ens ive ca l cu l a t i ons on t he da t a , and s t o r e t hose

ca l cu l a t i ons i n a mass s t o r age dev i ce o r d i sp l ay t he r e su l t s f o r human

use . The p rog rams u sed by t he mic rop roces so r a r e s t o r ed i n t he mass

s t o r age dev i ce and l oaded i n to RAM as t he u se r d i r e c t s . A f ew

mic rop roces so r p rog rams a r e s t o r ed i n ROM. The ROM-based

p rog rams a r e p r ima r i l y sma l l f i xed p rog rams t ha t ope ra t e pe r i phe ra l s

and o the r f i xed dev i ce s t ha t a r e connec t ed t o t he sy s t em. The de s ign

o f t he m ic rop roces so r i s d r i ven by t he de s i r e t o make i t a s expandab l e

and f l ex ib l e a s pos s ib l e , i n t he expec t a t i on o f commerc i a l succe s s i n

t he ma rke tp l ace .

Microcontro l l e r

Figu re .2 .4 B lock D iag ram o f Mic rocon t ro l l e r

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The above f i gu re shows t he b lock d i ag ram o f a t yp i ca l

m ic rocon t ro l l e r , wh i ch i s a t r ue compu te r on a ch ip . The de s ign

i nco rpo ra t e s a l l o f t he f e a tu r e s found i n a m ic rop roces so r CPU: ALU,

PC , SP , and r eg i s t e r . I t a l so ha s added o the r f e a tu r e s needed t o make

a comple t e compu te r : ROM, RAM, pa ra l l e l I /O , s e r i a l I /O , coun t e r s ,

and a c l ock c i r cu i t L ike t he mic rop roces so r , a m ic rocon t ro l l e r i s a

gene ra l - pu rpose dev i ce , bu t one t ha t i s mean t t o r e ad da t a , pe r fo rm

l im i t ed ca l cu l a t i ons . The p r ime u se o f a m ic ro -con t ro l l e r i s t o con t ro l

i t s env i ronmen t ba sed on t hose ca l cu l a t i ons . The p r ime u se o f a

m ic rocon t ro l l e r i s t o con t ro l t he ope ra t i on o f a mach ine u s ing a f i xed

p rog ram tha t i s s t o r ed i n ROM and t ha t does no t change ove r t he

l i f e t ime o f t he sy s t em.

The de s ign app roach o f t he m ic rocon t ro l l e r m i r ro r s t ha t o f t he

m ic rop roces so r : make a s i ng l e de s ign t ha t c an be u sed i n a s many

app l i c a t i ons a s pos s ib l e i n o rde r t o s e l l , hope fu l l y , a s many a s

pos s ib l e . The mic rop roces so r de s ign accompl i she s t h i s goa l by hav ing

a ve ry f l ex ib l e and ex t ens ive r epe r t o i r e o f mu l t i by t e i n s t ruc t i ons .

These i n s t ruc t i ons work i n a ha rdware con f igu ra t i on t ha t enab l e s

l a rge amoun t s o f memory and I /O t o be connec t ed t o add re s s and da t a

bus p in s on t he i n t eg ra t ed c i r cu i t package . Much o f t he a c t i v i t y i n t he

mic rop roces so r ha s t o do w i th mov ing code and da t a t o and f rom

ex t e rna l memory t o t he CPU. Many i n s t ruc t i ons a r e coup l ed w i th p in s

on t he i n t eg ra t ed c i r cu i t pakage ; t he p in s a r e p rog rammab le t ha t i s ,

c apab l e o f hav ing s eve ra l d i f f e r en t f unc t i ons depend ing on t he w i shes

o f t he p rog rammer . The mic rocon t ro l l e r i s conce rned w i th ge t t i ng

da t a f rom and t o i t s own p in s ; t he a r ch i t e c tu r e and i n s t ruc t i on s e t a r e

op t im ized t o hand l e da t a i n b i t and by t e s i z e .

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Microproces sors Vs Microcontro l l e r

The con t r a s t be tween a m ic rocon t ro l l e r and a m ic rop roces so r i s

be s t exempl i f i ed by t he f a c t t ha t mos t m ic rop roces so r s have many

ope ra t i ona l codes (opcodes ) f o r mov ing da t a f rom ex t e rna l memory t o

t he CPU; mic rocon t ro l l e r s may have one o r two . Mic rop roces so r s may

have one o r two t ypes o f b i t hand l i ng i n s t ruc t i ons ; m ic rocon t ro l l e r

w i l l have many .

The fundamen ta l d i f f e r ences be tween mic rop roces so r s and

mic rocon t ro l l e r s a r e t he se :

Mic rop roces so r s r e i n t ended t o be gene ra l pu rpose d ig i t a l

compu te r s whe rea s m ic rocon t ro l l e r s a r e i n t ended t o be spec i a l

pu rpose d ig i t a l con t ro l l e r s .

Microp roces so r s con t a in a CPU, memory add re s s ing c i r cu i t s , and

i n t e r rup t hand l i ng c i r cu i t s . Mic rocon t ro l l e r s have t he se f e a tu r e s a s

we l l a s t ime r s , pa r a l l e l and s e r i a l I /O , and s e r i a l I /O , and i n t e rna l

RAM and ROM.

Microcon t ro l l e r mode l s va ry i n da t a s i z e f rom 4 t o 32 b i t s . Fou r b i t

un i t s a r e p roduced i n huge vo lumes fo r ve ry s imp le app l i c a t i ons ,

and 8 -b i t un i t s a r e t he mos t ve r sa t i l e . S ix t een and 32 b i t un i t s a r e

u sed i n h igh speed con t ro l and s i gna l p roce s s ing app l i c a t i ons

Many mode l s f e a tu r e p rog rammab le p in s t ha t a l l ow ex t e rna l

memory t o be added w i th t he l o s s o f I /O capac i t y .

Eight b i t Microcontro l l e r s

15

Eigh t b i t ha s p roven t o be a ve ry u se fu l wor ld s i z e fo r sma l l

compu t ing t a sks .1 - by t e word i s adequa t e fo r many con t ro l and

mon i to r i ng app l i c a t i ons . Se r i a l ASCI I da t a i s a l so s t o r ed i n by t e

s i z e s , mak ing 8 b i t s t he na tu r a l cho i ce fo r da t a commun ica t i ons . Mos t

i n t eg ra t ed c i r cu i t memor i e s and many l og i c func t i ons a r e a r r anged i n

an 8 - b i t con f igu ra t i on t ha t i n t e r f ace s e a s i l y t o da t a bus se s o f 8 b i t s .

App l i c a t i on soph i s t i c a t i on can a l so r ange f rom s imp le app l i ance

con t ro l t o h igh speed mach ine con t ro l and da t a co l l e c t i on . Fo r t he se

r e a sons t he mic rocon t ro l l e r vendo r s have e s t ab l i shed ex t ens ive

f ami l i e s o f s im i l a r mode l s . A l l f e a tu r e a common l anguage , bu t d i f f e r

i n t he amoun t o f i n t e rna l ROM, RAM, and o the r cos t s ens i t i ve

f e a tu r e s . Of t en t he memory can be expanded t o i nc lude o f f - ch ip ROM

and RAM; i n some ca se s , t he m ic rocon t ro l l e r ha s no on -boa rd ROM a t

a l l , o r t he ROM i s an e l e c t r i c a l l y r ep rog rammab le r e ad on ly memory

[EPROM] . The ROM l e s s o r EPROM ve r s ions c an be u sed by t he

de s igne r t o p ro to type t he app l i c a t i on , and t he de s igne r c an o rde r t he

ROM ve r s ion i n l a rge quan t i t i e s f rom the f a c to ry . Many t imes t he

ROM ve r s ion i s neve r u sed . The de s igne r makes t he ROM l e s s o r

EPROM des ign su f f i c i en t l y gene ra l so t ha t on con f igu ra t i on may be

u sed many t imes , o r p roduc t i on vo lumes neve r j u s t i f y t he cos t o f a

f a c to ry ROM imp lemen ta t i on . As a fu r t he r en t i c emen t fo r t he buye r ,

some f ami l i e s have member s w i th f ewe r ex t e rna l p in s t o sh r i nk t he

package and t he cos t ; o the r s have spec i a l f e a tu r e s such a s ana log - to -

d ig i t a l and d ig i t a l - t o - ana log conve r t e r s on t he ch ip .

8051 Der iva t ive s

16

Along t he way , t h i s 8031 a r ch i t e c tu r e ga ined env i ab l e ma rke t

a ccep t ance . Many s emiconduc to r manufac tu r e r s s t a r t ed e i t he r

manufac tu r i ng t he 8031 dev i ce s a s such ( In t e l was l i be r a l i n g iv ing

away l i c ense t o whoeve r a sked ) o r deve lop ing a new k ind o f

m ic rocon t ro l l e r s ba sed on 8031 co re a r ch i t e c tu r e .

Manufac tu r e r s mod i f i ed t he ba s i c 8031 a r ch i t e c tu r e and added

many new pe r iphe ra l f unc t i ons t o make t hem a t t r a c t i ve t o t he

de s igne r s . Because o f t he ru sh , e l e c t ron i c commun i ty s t a r t ed ge t t i ng a

va r i e t y o f 8031 ba sed dev i ce s w i th r ange o f op t i ons . To bea t t he

compe t i t i on , manufac tu r e r s deve loped d i f f e r en t m ic rocon t ro l l e r s w i th

many un ique f ea tu r e s . These pa r t s a r e popu l a r l y known a s ‘8031

De r iva t i ve s ’ . A lmos t eve ry decen t manufac tu r e r boas t ed o f hav ing an

8031 ba sed mic rocon t ro l l e r i n t he l i ne c a rd .

F i r s t ma jo r manufac tu r e r was t he Ph i l i p s who b rough t ou t more

t han 40 -50 de r i va t i ve s w i th a va r i e t y o f I /O op t i ons , memory

combina t i ons , and pe r i phe ra l f unc t i ons . Dev i ce s became ava i l ab l e i n

r egu l a r DIP and SMD packages . Wi th t he ba s i c 8031 co re , Ph i l i p s

po r t ed h igh capac i t y P rog ram Memory (up to 32K/64K) , i t s pa t en t ed

I2C in t e r f ace bus , 8 /10 b i t Ana log t o D ig i t a l Conve r t e r s , CAN Bus ,

Cap tu re and Compare r eg i s t e r s , Wa tch dog t ime r , PWM fac i l i t i e s and

e t c . More I /O po r t s ( a s many a s e i gh t po r t s ) , add i t i ona l t ime r / coun t e r ,

s e cond s e r i a l po r t was a l so made ava i l ab l e i n Ph i l i p s dev i ce s .

Apa r t f r om a l l t he se , Ph i l i p s deve loped many consumer dev i ce s

mean t f o r t e l e com, compu te r and TV app l i c a t i ons . A smar t c a rd

con t ro l l e r was a l so deve loped by i nco rpo ra t i ng a c ryp tog raph i c

eng ine . So Ph i l i p s c l e a r l y e s t ab l i shed i t s e l f a s t he ma rke t l e ade r i n

8031 de r i va t i ve s and s t i l l c a t e r s t o t h i s s egmen t .

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Then come Da l l a s s emiconduc to r . Da l l a s r ede s igned t he 8031

a r ch i t e c tu r e and e l im ina t ed was t e c l ock cyc l e s o f o r i g ina l co re and

made a l l i n s t ruc t i ons execu t ed i n l e s s c l ock cyc l e s (max imum o f 4 )

wh ich have t r ad i t i ona l l y t aken up to 12 c lock cyc l e s . So , c ame t he

b i r t h o f H igh speed 8031 De r iva t i ve s .

Da l l a s s emiconduc to r a l so ha s go t a r ange o f s ecu re

m ic rocon t ro l l e r s ba sed on 8031 co re . Th i s m ic rocon t ro l l e r f ami ly u se s

non vo l a t i l e RAM to keep bo th p rog ram and da t a . Because o f t h i s

RAM, t he con t ro l l e r g ive s t he In Sys t em Reprog ram ab i l i t y . Da l l a s

ha s combined t h i s m ic rocon t ro l l e r , SRAM and l i t h ium ce l l i n a s i ng l e

pack . Th i s dev i ce gua ran t ee s 10+ yea r s o f da t a r e t en t i on i n t he RAM

a rea . Th i s 8031 a l so boas t s t he t ampe r p roo f s ecu r i t y f e a tu r e s l i ke

Rea l T ime Memory Enc ryp t i on , u se r s e l e c t ed 48 b i t Enc ryp t i on key ,

memory con t en t s , s e cu r i t y l ock and t he f a c i l i t y t o h ide i n t e r rup t

vec to r t ab l e . As you can ag ree , t h i s pa r t i cu l a r 8031 dev i ce ha s found

a n i che marke t i n bank ing and s ecu r i t y r e l a t ed app l i c a t i ons .

A tme l Corpo ra t i on i s t he ma jo r s emiconduc to r manufac tu r e r who

i n t roduced many f l a sh memor i e s ba sed 8031 de r i va t i ve s a t a

compe t i t i ve cos t . A tme l u sed i t s expe r t i s e i n f l a sh memory t e chno logy

i n to t he ba s i c 8031 co re and b rough t ou t m ic rocon t ro l l e r s w i th a

va r i e t y o f f l a sh memory op t i ons and f ew dev i ce s a l so ca r ry In Sys t em

Reprog ramming f ac i l i t y . You can p rog ram/ rep rog ram th i s

m ic rocon t ro l l e r a f t e r so lde r i ng t he dev i ce i n t he t a rge t boa rd . I f t h i s

p rog ramming f ac i l i t y i s embedded i n t he sy s t em so f twa re , t hen t he

t a sks l i ke r emo te ca l i b r a t i on , ons i t e sy s t em upg rada t i on become a s

e a sy a s s end ing you r da t a /p rog ram in a f l oppy d i sk o r by i n t e rne t .

A tme l dev i ce s spo r t s ecu r i t y l ock t o i t s f l a sh memory t o p ro t ec t t he

con t en t s f rom the p ry ing eyes .

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Mean t ime , I n t e l i t s e l f t r i ed t o c a sh i n t he popu l a r i t y o f t h i s

8031 a r ch i t e c tu r e and i n t roduced improved ve r s i ons o f

m ic rocon t ro l l e r s : 80151 and 80251 f ami l i e s . These dev i ce s spo r t 16

b i t a r ch i t e c tu r e u s ing 8031 co re and un fo r tuna t e ly t he se dev i ce s have

no t become a s popu l a r a s 8031 .Even a f t e r many yea r s o f i n t roduc t i on ,

8031 co re i s s t i l l go ing s t rong i n 8 b i t a r ena .

Addres s ing Modes

8031 ' s a s semb ly l anguage i n s t ruc t i on s e t cons i s t s o f an

ope ra t i on mnemon ic and ze ro t o t h r ee ope rands s epa ra t ed by commas .

I n two by t e i n s t ruc t i ons t he de s t i na t i on i s spec i f i ed f i r s t , and t hen t he

sou rce . By t e w ide mnemon ic s l i ke ADD o r MOV use t he Accumula to r

a s a sou rce ope rand and a l so t o r e ce ive t he r e su l t .

The 8031 suppo r t s f i ve t ypes o f add re s s ing modes :

1 . Reg i s t e r Addre s s ing

2 . D i r ec t Addre s s ing

3 . Reg i s t e r I nd i r ec t Addre s s ing

4 . Immed ia t e Addre s s ing

5 . I ndex Addre s s ing

Reg i s t er Addres s ing

Reg i s t e r Addre s s ing acce s se s t he e i gh t work ing r eg i s t e r s (R0

R7) o f t he s e l ec t ed r eg i s t e r bank . The l e a s t s i gn i f i c an t t h r ee b i t s o f

t he i n s t ruc t i on opcode i nd i ca t e wh ich r eg i s t e r i s t o be u sed fo r t he

ope ra t i on . One o f t he fou r banks o f r eg i s t e r s i s t o be p r ede f ined i n

t he PSW be fo re u s ing r eg i s t e r add re s s ing i n s t ruc t i on . ACC, B , DPTR

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and CY, ( t he Boo l ean Accumula to r ) c an a l so be add re s sed i n t h i s

mode .

Direc t Addres s ing

Di rec t add re s s ing can acce s s any on ch ip va r i ab l e s o r ha rdware

r eg i s t e r . To i nd i ca t e t he add re s s o f t he l oca t i on , an add i t i ona l by t e i s

a t t a ched t o t he opcode . Depend ing on t he h ighes t o rde r b i t o f t he

d i r ec t add re s s by t e one o f two phys i ca l memory space i s s e l e c t ed .

When t he d i r ec t add re s s r ange i s be tween 0 and 127 (00H

7FH) one o f t he 128 l ow o rde r on ch ip RAM loca t i on i s a cce s sed . A l l

I /O po r t s , spec i a l f unc t i on , con t ro l r eg i s t e r s a r e a s s i gned be tween 128

and 255 (80H FFH) . When d i r ec t add re s s ing i nd i ca t e s any l oca t i on

i n t h i s r ange , co r r e spond ing ha rdware r eg i s t e r i s a cce s sed .

Th i s i s t he on ly me thod ava i l ab l e fo r a cce s s ing I /O po r t s and

spec i a l f unc t i on r eg i s t e r s .

Reg i s t er Ind irec t Addres s ing

Reg i s t e r i nd i r ec t add re s s ing u se s t he con t en t s o f e i t he r R0 o r

R1 ( i n t he p r e s e l ec t ed r eg i s t e r bank ) a s a add re s s po in t e r t o l oca t e i n

a 256 by t e b lock ( t he l ower 128 by t e s o f i n t e rna l RAM in 8031 o r 256

by t e s i n 8032 ) o r t he l ower 256 by t e s o f ex t e rna l da t a memory . No te

t ha t t he spec i a l f unc t i on r eg i s t e r s a r e no t a cce s s ib l e i n t h i s mode .

Acces s t o fu l l 64K ex t e rna l da t a memory add re s s space i s i nd i ca t ed by

t he 16 b i t Da t a Po in t e r r eg i s t e r , DPTR.

Execu t i on o f PUSH and POP in s t ruc t i ons a l so i nvo lve i nd i r ec t

r eg i s t e r add re s s ing . The S t ack Po in t e r i nd i ca t e s t he co r r ec t s t a ck

l oca t i on anywhe re i n t he i n t e rna l RAM.

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Immedia te Addres s ing

When a sou rce ope rand i s a cons t an t r a t he r t han a va r i ab l e ,

t hen t he cons t an t c an be embedded i n to t he i n s t ruc t i on i t s e l f . Th i s

k ind o f i n s t ruc t i ons t ake s two by t e s and f i r s t one spec i f i e s t he opcode

and s econd by t e g ive s t he r equ i r ed cons t an t .

Index Addres s ing

Only t he P rog ram Memory can be acce s sed by t h i s mode . Th i s

mode i s i n t ended fo r r e ad ing l ookup t ab l e s i n t he P rog ram Memory . A

16 b i t ba se r eg i s t e r ( e i t he r DPTR o r t he P rog ram Coun te r ) po in t s t o

t he ba se o f t he l ookup t ab l e s and t he Accumula to r c a r r i e s t he cons t an t

i nd i ca t i ng t ab l e en t ry number .

Microcontro l l e r s for Embedded Sys tems

In t he L i t e r a tu r e d i s cus s ing mic rop roces so r s , we o f t en s ee t he

t e rm Embedded Sys t em. Mic rop roces so r s and Mic rocon t ro l l e r s a r e

w ide ly u sed i n embedded sys t em p roduc t s . An embedded sys t em

p roduc t u se s a m ic rop roces so r (o r Mic rocon t ro l l e r ) t o do one t a sk

on ly . A p r i n t e r i s an example o f embedded sys t em s ince t he p roce s so r

i n s ide i t pe r fo rms one t a sk on ly ; name ly ge t t i ng t he da t a and p r i n t i ng

i t . Con t r a s t t h i s w i th a Pen t i um based PC . A PC can be u sed fo r any

number o f app l i c a t i ons such a s word p roce s so r , p r i n t - s e rve r , bank

t e l l e r t e rmina l , V ideo game , ne twork s e rve r , o r I n t e rne t t e rmina l .

So f twa re fo r a va r i e t y o f app l i c a t i ons c an be l oaded and run . Of

cou r se t he r e a son a pc can pe r fo rm myr i ad t a sks i s t ha t i t h a s RAM

memory and an ope ra t i ng sy s t em tha t l oads t he app l i c a t i on so f twa re

i n to RAM memory and l e t s t he CPU run i t .

I n an Embedded sys t em, t he r e i s on ly one app l i c a t i on so f twa re

t ha t i s t yp i ca l l y bu rned i n to ROM. An x86 PC con t a in s o r i s

21

connec t ed t o va r i ous embedded p roduc t s such a s keyboa rd , p r i n t e r ,

modem, d i sk con t ro l l e r , sound ca rd , CD-ROM dr ive s , mouse , and so

on . Each one o f t he se pe r i phe ra l s ha s a Mic rocon t ro l l e r i n s ide i t t ha t

pe r fo rms on ly one t a sk . Fo r example , i n s ide eve ry mouse t he r e i s a

Mic rocon t ro l l e r t o pe r fo rm the t a sk o f f i nd ing t he mouse pos i t i on and

s end ing i t t o t he PC .

6 . VOLTAGE CONVERTER

Thi s i s u sed t o conve r t TTL log i c vo l t age i n to RS232

vo l t age .

TTL Log i c : l og i c 1= 5v

l og i c 0= GND

RS232 : l og i c 1= +9v

l og i c 0= -9v

IC MAX232 i s u sed a s vo l t age conve r t e r . An ex t e rna l c ry s t a l

o sc i l l a t o r i s u sed fo r i t s ope ra t i on .

7 . PC SERIAL PORT

Thi s po r t i s u sed t o ge t da t a f rom mic rocon t ro l l e r t o pe r sona l

compu te r i n s e r i a l manne r . A l l IBM PC and compa t i b l e compu te r s a r e

t yp i ca l l y equ ipped w i th two se r i a l po r t s and one pa ra l l e l po r t .

A l t hough t he se two t ypes o f po r t s a r e u sed fo r commun ica t i ng w i th

ex t e rna l dev i ce s , t hey work i n d i f f e r en t ways .

A pa ra l l e l po r t s ends and r ece ive s da t a e i gh t b i t s a t a t ime ove r

8 s epa ra t e w i r e s . Th i s a l l ows da t a t o be t r ans f e r r ed ve ry qu i ck ly ;

howeve r , t he c ab l e r equ i r ed i s more bu lky because o f t he number o f

22

i nd iv idua l w i r e s i t mus t con t a in . Pa r a l l e l po r t s a r e t yp i ca l l y u sed t o

connec t a PC to a p r i n t e r and a r e r a r e ly u sed fo r much e l s e . A s e r i a l

po r t s ends and r ece ive s da t a one b i t a t a t ime ove r one w i r e . Whi l e i t

t ake s e i gh t t imes a s l ong t o t r ans f e r e ach by t e o f da t a t h i s way , on ly a

f ew wi r e s a r e r equ i r ed .

I n f a c t , two-way ( fu l l dup l ex ) commun ica t i ons i s pos s ib l e w i th

on ly t h r ee s epa ra t e w i r e s - one t o s end , one t o r e ce ive , and a common

s igna l g round w i r e .

8 . INTERFACING CIRCUIT

Thi s i s u sed t o i n t e r f ace t he aud io s i gna l f r om the

compu te r t o t he t e l ephone l i ne .

3 . HARDWARE DECSRIPTION

3.1 MICROCONTROLLER

The AT89C2051 i s a l ow-vo l t age , h igh -pe r fo rmance CMOS 8 -b i t

m ic rocompu te r w i th 2 Kby te s o f F l a sh p rog rammab le and e r a sab l e

23

r e ad on ly memory (PEROM) . The dev i ce i s manufac tu r ed u s ing

A tme l ’ s h igh dens i t y nonvo l a t i l e memory t e chno logy and i s

compa t i b l e w i th t he i ndus t ry s t anda rd MCS-51 i n s t ruc t i on s e t and

p inou t . By combin ing a ve r sa t i l e 8 -b i t CPU wi th F l a sh on a

mono l i t h i c ch ip , t he A tme l AT89C2051 i s a power fu l m ic rocompu te r

wh ich p rov ide s a h igh ly f l ex ib l e and cos t e f f ec t i ve so lu t i on t o many

embedded con t ro l app l i c a t i ons .

The AT89C2051 p rov ide s t he fo l l owing s t anda rd f ea tu r e s : 2

Kby te s o f F l a sh , 128 by t e s o f RAM, 15 I /O l i ne s , two 16 -b i t

t ime r / coun t e r s , f i ve vec to r two- l eve l i n t e r rup t a r ch i t e c tu r e , a f u l l

dup l ex s e r i a l po r t , a p r ec i s i on ana log compa ra to r , on -ch ip o sc i l l a t o r

and c lock c i r cu i t r y .

I n add i t i on , t he AT89C2051 i s de s igned w i th s t a t i c l og i c fo r

ope ra t i on down to z e ro f r equency and suppo r t s two so f twa re

s e l ec t ab l e power s av ing modes . The Id l e Mode s t ops t he CPU wh i l e

a l l owing t he RAM, t ime r / coun t e r s , s e r i a l po r t and i n t e r rup t sy s t em to

con t i nue func t i on ing . The Power Down Mode s aves t he RAM con t en t s

bu t f r e eze s t he o sc i l l a t o r d i s ab l i ng a l l o t he r ch ip func t i ons un t i l t he

nex t ha rdware r e se t .

3 .1 .1 P in Conf igura t ion

The mic rocon t ro l l e r AT89C2051 i s ava i l ab l e i n 20 p in Dua l

I n l i ne Package (DIP) .

24

F igu re .3 .1 P in d i ag ram o f AT89C2051

3 .1 .2 B lock D iagram

25

F igu re .3 .2 B lock D iag ram o f AT89C2051

26

3 .1 .3 P in Descr ip t ion

VCC

Supp ly vo l t age .

GND

Ground .

Por t 1

Po r t 1 i s an 8 -b i t b id i r ec t i ona l I /O po r t . Po r t p in s P1 .2 t o P1 .7

p rov ide i n t e rna l pu l l ups . P1 .0 and P1 .1 r equ i r e ex t e rna l pu l l ups . P1 .0

and P1 .1 a l so s e rve a s t he pos i t i ve i npu t (AIN0) and t he nega t i ve

i npu t (AIN1) , r e spec t i ve ly , o f t he on -ch ip p r ec i s i on ana log

compa ra to r . The Po r t 1 ou tpu t bu f f e r s c an s i nk 20 mA and can d r i ve

LED d i sp l ays d i r ec t l y . When 1 s a r e wr i t t en t o Po r t 1 p in s , t hey can be

u sed a s i npu t s . When p in s P1 .2 t o P1 .7 a r e u sed a s i npu t s and a r e

ex t e rna l l y pu l l ed l ow , t hey w i l l sou rce cu r r en t ( I IL ) because o f t he

i n t e rna l pu l l ups . Po r t 1 a l so r e ce ive s code da t a du r ing F l a sh

p rog ramming and p rog ram ve r i f i c a t i on .

Por t 3

Po r t 3 p in s P3 .0 t o P3 .5 , P3 .7 a r e s even b id i r ec t i ona l I /O p in s

w i th i n t e rna l pu l l -ups . P3 .6 i s ha rd -wi r ed a s an i npu t t o t he ou tpu t o f

t he on -ch ip compa ra to r and i s no t a cce s s ib l e a s a gene ra l pu rpose I /O

p in . The Po r t 3 ou tpu t bu f f e r s c an s i nk 20 mA. When 1s a r e wr i t t en t o

Po r t 3 p in s t hey a r e pu l l ed h igh by t he i n t e rna l pu l l -ups and can be

u sed a s i npu t s . As i npu t s , Po r t 3 p in s t ha t a r e ex t e rna l l y be ing pu l l ed

l ow wi l l sou rce cu r r en t ( I IL ) because o f t he pu l l -ups . Po r t 3 a l so

s e rve s t he func t i ons o f va r i ous spec i a l f e a tu r e s o f t he AT89C2051 a s

l i s t ed be low:

27

Tab le 3 .1 A l t e rna t e Func t i ons o f po r t 3

Po r t 3 a l so r e ce ive s some con t ro l s i gna l s f o r F l a sh p rog ramming and

p rog ramming ve r i f i c a t i on .

RST

Rese t i npu t . A l l I /O p in s a r e r e se t t o 1 s a s soon a s RST goes

h igh . Ho ld ing t he RST p in h igh fo r two mach ine cyc l e s wh i l e t he

o sc i l l a t o r i s r unn ing r e se t s t he dev i ce . Each mach ine cyc l e t ake s 12

o sc i l l a t o r o r c l ock cyc l e s .

XTAL1

Inpu t t o t he i nve r t i ng o sc i l l a t o r amp l i f i e r and i npu t t o t he

i n t e rna l c l ock ope ra t i ng c i r cu i t .

XTAL2

Outpu t f rom the i nve r t i ng o sc i l l a t o r amp l i f i e r .

28

3 .1 .4 Osc i l l a tor Charac ter i s t i c s

XTAL1 and XTAL2 a r e t he i npu t and ou tpu t , r e spec t i ve ly , o f an

i nve r t i ng amp l i f i e r wh ich can be con f igu red fo r u se a s an on -ch ip

o sc i l l a t o r , a s shown in F igu re 1 . E i t he r a qua r t z c ry s t a l o r c e r amic

r e sona to r may be u sed . To d r i ve t he dev i ce f rom an ex t e rna l c l ock

sou rce , XTAL2 shou ld be l e f t unconnec t ed wh i l e XTAL1 i s d r i ven a s

shown in F igu re 2 . The re a r e no r equ i r emen t s on t he du ty cyc l e o f t he

ex t e rna l c l ock s i gna l , s i nce t he i npu t t o t he i n t e rna l c l ock ing c i r cu i t r y

i s t h rough a d iv ide by - two f l i p - f l ops , bu t m in imum and max imum

vo l t age h igh and l ow t ime spec i f i c a t i ons mus t be obse rved .

Figure.3.3 Oscillator Connections

3 .2 DTMF Decoder

The MT8870 i s a s i ng l e ch ip DTMF rece ive r i n co rpo ra t i ng

sw i t ched capac i t o r f i l t e r t e chno logy and an advanced d ig i t a l

coun t i ng / ave rag ing a lgo r i t hm fo r pe r i od measu remen t . The

29

func t i ona l b lock d i ag ram o f MT8870 i s shown in t he be low f i gu re

dep i c t s t he i n t e rna l work ing o f t h i s dev i ce .

F igu re .3 .4 Func t i ona l d i ag ram o f IC MT8870

The DTMF s igna l i s f i r s t bu f f e r ed by i npu t op -amp tha t a l l ows

ad ju s tmen t ga in and cho i ce o f i npu t con f igu ra t i on . The i npu t s t age i s

f o l l owed by a l ow pas s RC ac t i ve f i l t e r , wh i ch pe r fo rms an t a l i a s i ng

func t i on . D ia l t one a t 350 and 440Hz i s t hen r e j e c t ed by a 3 r d o rde r

sw i t ched capac i t o r no t ch f i l t e r . The s i gna l i s s t i l l i n i t s i nd iv idua l

componen t s by two 6 t h o rde r sw i t ched capac i t o r band pa s s f i l t e r . Each

componen t smoo thed by an ou tpu t f i l t e r and squa red by a ha rd

l im i t i ng compa ra to r . The two r e su l t i ng r ec t angu l a r wave fo rms a r e

t hen app l i ed t o a d ig i t a l c i r cu i t , whe re a coun t i ng a lgo r i t hm measu re s

30

and ave rages t he r e pe r i ods . An accu ra t e r e f e r ence c lock i s de r i ved

f rom an i nexpens ive ex t e rna l 3 . 58MHz c rys t a l .

The t ime r equ i r ed t o de t ec t a va l i d t one pa i r t dP i s a f unc t i on o f

decode a lgo r i t hm, t one f r equency , and t he p r ev ious s t a t e o f t he

decoded l og i c . Es t ( e a r l y , s t e e r i ng ou tpu t ) i nd i ca t e s t ha t two t ones o f

va l i d f r equency have been de t ec t ed and i n i t i a t e s an RC t im ing c i r cu i t .

I f bo th t ones a r e p r e sen t f o r a m in imum gua rd t ime , de t e rmined by an

ex t e rna l RC ne twork , t he DTMF s igna l i s decoded and t he r e su l t i ng

da t a l a t ched on t he ou tpu t r eg i s t e r . The de l ayed s t e e r i ng ou tpu t ( s tD)

i s r a i s ed t o i nd i ca t e t ha t new da t a i s ava i l ab l e . (The ou tpu t

co r r e spond ing t o e ach key p r e s sed i s shown in t he t r u th t ab l e )

3 .2 .1Tone de tec t i on

Af te r r e ce iv ing a DTMF tone t he DTMF decode r (MT8870)

p l ace s t he co r r e spond ing b ina ry number on i t s ou t pu t (S tD) goes h igh

t o s t a t e t ha t new da t a i s ava i l ab l e . The de t ec t i on o f t he de l ayed

s t e e r i ng ou tpu t i s t o t he du ra t i on o f t he r e ce ived DTMF rece ive r ha s

a l r e ady been exp l a ined .

31

3 .2 .2 PIN DIAGRAM OF IC MT8870

Figu re .3 .5 Pin Diagram o f IC MT8870

32

Pin Descr ip t ion

Tab le .3 .2 P in de sc r i p t i on o f IC MT8870

33

Recommended Opera t ing Cond i t i on

Tab le : 3 . 3 Ope ra t i ng cond i t i ons o f IC MT8870

3 .2 .3 Func t iona l Descr ip t ion

The MT8870D/MT8870D-1 mono l i t h i c DTMF rece ive r

o f f e r s sma l l s i z e , l ow power consumpt ion and h igh pe r fo rmance .

I t s a r ch i t e c tu r e cons i s t s o f a band sp l i t f i l t e r s ec t i on , wh ich

s epa ra t e s t he h igh and l ow g roup t ones , f o l l owed by a d ig i t a l

coun t i ng s ec t i on wh ich ve r i f i e s t he f r equency and du ra t i on o f t he

r e ce ived t ones be fo re pa s s ing t he co r r e spond ing code t o t he

ou tpu t bus .

Fi l t er Sec t i on

Sepa ra t i on o f t he l ow-g roup and h igh g roup t ones i s a ch i eved

by app ly ing t he DTMF s igna l t o t he i npu t s o f two s i x th -o rde r

sw i t ched capac i t o r band pa s s f i l t e r s , t he bandwid th s o f wh ich

co r r e spond t o t he l ow and h igh g roup f r equenc i e s . The f i l t e r s ec t i on

a l so i nco rpo ra t e s no t ches a t 350 and 440 Hz fo r excep t i ona l d i a l

34

t one r e j e c t i on ( s ee F igu re 3 ) . Each f i l t e r ou tpu t i s f o l l owed by a

s i ng l e o rde r sw i t ched capac i t o r f i l t e r s ec t i on wh ich smoo thes t he

s i gna l s p r i o r t o l im i t i ng . L imi t i ng i s pe r fo rmed by h igh -ga in

compa ra to r s wh ich a r e p rov ided w i th hys t e r e s i s t o p r even t de t ec t i on

o f unwan ted l ow- l eve l s i gna l s . The ou tpu t s o f t he compa ra to r s

p rov ide fu l l r a i l l og i c sw ings a t t he f r equenc i e s o f t he i ncoming

DTMF s igna l s .

Decoder Sec t ion

Fo l lowing t he f i l t e r s ec t i on i s a decode r emp loy ing d ig i t a l

coun t i ng t e chn iques t o de t e rmine t he F requenc i e s o f t he i ncoming

t ones and t o ve r i fy t ha t t hey co r r e spond t o s t anda rd DTMF

f r equenc i e s . A complex ave rag ing a lgo r i t hm p ro t ec t s aga in s t t one

s imu la t i on by ex t r aneous s i gna l s such a s vo i ce wh i l e p rov id ing

t o l e r ance t o sma l l f r equency dev i a t i on and va r i a t i ons . Th i s ave rag ing

a lgo r i t hm has been deve loped t o ensu re an op t imum combina t i on o f

immun i ty t o t a l k -o f f and t o l e r ance t o t he p r e sence o f i n t e r f e r i ng

f r equenc i e s ( t h i rd t ones ) and no i s e . When t he de t ec to r r e cogn i ze s t he

p r e sence o f two va l i d t ones ( t h i s i s r e f e r r ed t o a s t he “ s i gna l

cond i t i on” i n some i ndus t ry spec i f i c a t i ons ) t he “Ea r ly S t ee r i ng” (ES t )

ou tpu t w i l l go t o an ac t i ve s t a t e . Any subsequen t l o s s o f s i gna l

cond i t i on w i l l c ause ES t t o a s sume an i nac t i ve s t a t e . The s t e e r i ng

c i r cu i t works i n r eve r se t o va l i da t e t he i n t e r d ig i t pause be tween

s i gna l s . Thus , a s we l l a s r e j e c t i ng s i gna l s t oo sho r t t o be cons ide red

va l i d , t he r e ce ive r w i l l t o l e r a t e s i gna l i n t e r rup t i ons (d ropou t ) t oo

sho r t t o be cons ide red a va l i d pause . Th i s f a c i l i t y , t oge the r w i th t he

c apab i l i t y o f s e l e c t i ng t he s t e e r i ng t ime cons t an t s ex t e rna l l y , a l l ows

t he de s igne r t o t a i l o r pe r fo rmance t o mee t a w ide va r i e t y o f sy s t em

r equ i r emen t s .

35

3 .2 .4 Guard T ime Adjus tment

In many s i t ua t i ons no t r equ i r i ng s e l ec t i on o f t one du ra t i on and

i n t e r d ig i t a l pause , t he s imp le s t e e r i ng c i r cu i t shown in F igu re 4 i s

app l i c ab l e . Componen t va lue s a r e chosen acco rd ing t o t he fo rmu la :

tREC=tDP+tGTP

t ID= tDA+tGTA

The va lue o f tDP i s a dev i ce pa r ame te r and tREC i s t he

m in imum s igna l du ra t i on t o be r e cogn i zed by t he r e ce ive r . D i f f e r en t

s t e e r i ng a r r angemen t s may be u sed t o s e l ec t i ndependen t l y t he gua rd

t imes fo r t one P re sen t ( tGTP) and t one absen t ( tGTA) . Th i s may be

nece s sa ry t o mee t sy s t em spec i f i c a t i ons wh ich p l ace bo th accep t and

r e j e c t l im i t s on bo th t one du ra t i on and i n t e rd ig i t a l pause . Gua rd t ime

ad ju s tmen t a l so a l l ows t he de s igne r t o t a i l o r sy s t em pa rame te r s such

a s t a l k o f f and no i s e immun i ty . I nc r ea s ing tREC improves t a l k -o f f

pe r fo rmance s i nce i t r educes t he p robab i l i t y t ha t t ones s imu la t ed by

speech w i l l ma in t a in s i gna l cond i t i on l ong enough t o be r eg i s t e r ed .

A l t e rna t i ve ly , a r e l a t i ve ly sho r t tREC wi th a l ong tDO wou ld be

app rop r i a t e f o r ex t r eme ly no i sy . Env i ronmen t s such a s f a s t

a cqu i s i t i on t ime and immun i ty t o t one d rop -ou t s a r e r equ i r ed .

Power -down and Inh ib i t Mode

A log i c h igh app l i ed t o p in 6 (PWDN) wi l l power down the

dev i ce t o m in imize t he power consumpt ion i n a S t and by mode . I t

s t ops t he o sc i l l a t o r and t he func t i ons o f t he f i l t e r s . I nh ib i t mode i s

enab l ed by a l og i c h igh i npu t t o t he p in 5 ( INH) . I t i nh ib i t s t he

de t ec t i on o f t ones r ep re sen t i ng cha rac t e r s A , B , C , and D . The ou tpu t

code w i l l r ema in t he s ame a s t he p r ev ious de t ec t ed code .

36

Di f f erent ia l Input Conf igura t ion

The i npu t a r r angemen t o f t he MT8870D/MT8870D-1 p rov ide s a

d i f f e r en t i a l - i npu t ope ra t i ona l amp l i f i e r a s we l l a s a b i a s sou rce

(VRef ) wh ich i s u sed t o b i a s t he i npu t s a t m id - r a i l . P rov i s i on i s made

fo r connec t i on o f a f e edback r e s i s t o r t o t he op -amp ou tpu t (GS) fo r

ad ju s tmen t o f ga in . I n a s i ng l e - ended con f igu ra t i on , t he i npu t p in s a r e

connec t ed a s shown in F igu re 10 w i th t he op -amp connec t ed fo r un i t y

ga in and VRef b i a s ing t he i npu t a t 1 /2VDD. F igu re 6 shows t he

d i f f e r en t i a l con f igu ra t i on , wh ich pe rmi t s t he ad ju s tmen t o f ga in w i th

t he f e edback r e s i s t o r .

Crys ta l Osc i l l a tor

The i n t e rna l c l ock c i r cu i t i s comple t ed w i th t he add i t i on o f an

ex t e rna l 3 . 579545 MHz c rys t a l and i s no rma l ly connec t ed a s shown in

F igu re (S ing l e - Ended Inpu t Conf igu ra t i on ) .Howeve r ; i t i s pos s ib l e t o

con f igu re s eve ra l MT8870D/MT8870D-1 dev i ce s emp loy ing on ly a

s i ng l e o sc i l l a t o r c ry s t a l . The o sc i l l a t o r ou tpu t o f t he f i r s t dev i ce i n

t he cha in i s coup l ed t h rough a 30 pF capac i t o r t o t he o sc i l l a t o r i npu t

(OSC1) o f t he nex t dev i ce . Subsequen t dev i ce s a r e connec t ed i n a

s im i l a r f a sh ion . The p rob l ems a s soc i a t ed w i th unba l anced l oad ing a r e

no t a conce rn w i th t he a r r angemen t shown , i . e . , p r ec i s i on ba l anc ing

capac i t o r s a r e no t r equ i r ed .

37

3 .2 .5 Tone Decod ing o f MT8870

Tab l e 3 .4 : Tone Decod ing o f MT8870

3 .2 .6 Fea tures

• Comple t e DTMF Rece ive r r e commended fo r mos t app l i c a t i ons ,

l e av ing R t o be s e l ec t ed by t he de s igne r

• Low power consumpt ion

• In t e rna l ga in s e t t i ng amp l i f i e r

• Cen t r a l o f f i c e qua l i t y

• Power -down mode

38

• I nh ib i t mode

• Backward compa t i b l e w i th MT8870C/MT8870C-1

3 .2 .7 App l i ca t ions

• Pag ing sy s t ems

• Repea t e r sy s t ems /mob i l e r ad io

• C red i t c a rd sy s t ems

• Remote con t ro l

• Pe r sona l compu te r s

• Te l ephone answer ing mach ine

3 .3 VOLTAGE CONVERTER (MAX232)

The MAX220–MAX249 f ami ly o f l i ne d r i ve r s / r e ce ive r s i s

i n t ended fo r a l l E IA/TIA-232E and V .28 /V .24 commun ica t i ons

i n t e r f ace s , pa r t i cu l a r l y app l i c a t i ons whe re ±12V i s no t ava i l ab l e .

These pa r t s a r e e spec i a l l y u se fu l i n ba t t e ry -powered sy s t ems , s i nce

t he i r l ow-power shu tdown mode r educes power d i s s i pa t i on t o l e s s

t han 5μW.

Feature

Opera t e f rom S ing l e +5V Power Supp ly

Low-Power Rece ive Mode i n Shu tdown

Mee t A l l E IA/TIA-232E and V .28 Spec i f i c a t i ons

Mul t i p l e Dr ive r s and Rece ive r s

3-S t a t e Dr ive r and Rece ive r Ou tpu t s

39

3 .3 .1 PIN Diagram

Figu re .3 .6 P in D iag ram o f MAX232

S ince t he RS232 i s no t compa t i b l e w i th t oday ’ s m ic rop roces so r s

and mic rocon t ro l l e r s , we need a l i ne d r i ve r ( vo l t age conve r t e r ) t o

conve r t t he RS232’ s s i gna l s t o TTL vo l t age l eve l s t ha t w i l l be

a ccep t ab l e t o t he 8051 ’ s TxD and RxD p in s . One example o f such a

conve r t e r i s MAX232 f rom Max im Corp . The MAX 232 conve r t s f r om

RS232 vo l t age l eve l s t o TTL vo l t age l eve l s , and v i ce ve r sa . One

advan t age o f t he MAX232 ch ip i s t ha t i t u se s a+5V power sou rce

wh ich i s t he s ame a s t he sou rce vo l t age fo r t he 8051 . I n o the r words ,

w i th a s i ng l e +5 V power supp ly we can power bo th t he 80551 and

MAX232 , w i th no need fo r t he dua l power supp l i e s t ha t a r e common

in many o lde r sy s t ems .

40

3 .3 .2 Func t i ona l D iag ram o f MAX232

Figu re .3 .7 Func t i ona l D iag ram o f MAX232

The MAX232 ha s two se t s o f l i ne d r i ve r s f o r t r ans f e r r i ng and

r ece iv ing da t a , a s shown in F igu re 10 -7 . The l i ne d r i ve r s u sed fo r

TxD a re c a l l ed T1 and T2 wh i l e t he l i ne d r i ve r s f o r Rxd a r e

de s igna t ed a s R1 and R2 . I n many app l i c a t i ons on ly one o f e ach i s

u sed fo r example , T1 and R1 a r e u sed t oge the r f o r TxD and RxD o f

t he 8051 and t he s econd s e t i s l e f t unused . No t i c e i n MAX232 t ha t t he

T1 l i ne d r i ve r ha s a de s igna t i on o f T1 i n and T1 ou t on p in number s

41

11 and 14 , r e spec t i ve ly . The T1 i n p in i s t he TTL s ide and i s

connec t ed t o TxD o f t he mic rocon t ro l l e r , wh i l e T1 ou t i s t he RS232

s i de t ha t i s connec t ed t o t he RxD p in o f t he RS232 DB connec to r .

The R1 l i ne d r i ve r ha s a de s igna t i on o f R1 i n and R i ou t on p in

number s 13 and 12 , r e spec t i ve ly . The R1 i n (p in 13 ) i s t he RS232 s i de

t ha t i s connec t ed t o t he TxD p in o f t he RS232 DB connec to r , and R1

ou t ( p in 12 ) i s t he TTL s ide t ha t i s connec t ed t o t he RxD p in o f t he

m ic rocon t ro l l e r . See f i gu re 10 -7 . No t i c e t he nu l l modem connec t i on

whe re RxD fo r one i s TxD fo r t he o the r .

MAX232 r equ i r e s fou r c apac i t o r s r ang ing f rom 1 t o 22F . The

mos t w ide ly u sed va lue fo r t he se c apac i t o r s i s 22n f .

3 .3 .3 APPLICATIONS

Por t ab l e Compu te r s

Low-Power Modems

In t e r f ace T rans l a t i on

Ba t t e ry -Powered RS-232 Sys t ems

Mul t i d rop RS-232 Ne tworks

42

4 . CIRCUIT DIAGRAM

Figu re .4 .1 C i r cu i t D i ag ram

43

4 .1 CIRCUIT OPERATION

When t he t e l ephone r i ng a r r i ve s t he r i ng s enso r de t ec t s i t and i t

w i l l s end a s i gna l t o t he mic rocon t ro l l e r . The Mic rocon t ro l l e r w i l l

t hen t ake t he phone w i th he lp o f ON/OFF hook s imu la to r and i t w i l l

s ense t he DTMF s igna l and i t w i l l ge t t he DTMF s igna l and t he

Mic rocon t ro l l e r w i l l sw i t ch on t he co r r e spond ing Re l ay .

A t no rma l t ime t he vo l t age ac ros s t he t e l ephone l i ne i s 48v and

when a r i ng a r r i ve s t hen a vo l t age o f 74v AC i s i n j e c t ed t h rough t he

t e l ephone and t h i s AC wi l l pa s s t h rough t he capac i t o r C4 and t hough

t he zene r d iodes t o t he LED in t he op tocoup l e r and i t w i l l conduc t

and t h i s l i gh t w i l l conduc t t he pho to t r ans i s t o r and t he r e fo re a l ow

s igna l was f ed t o t he mic rocon t ro l l e r and i t w i l l t hen sw i t ch on t he

Hook Re l ay o f a t e l ephone .

The DTMF rece ive r w i l l decode t he t one s i gna l i n to d ig i t a l

wh i ch was f ed t o t he mic rocon t ro l l e r f o r f u r t he r con t ro l . The ma in

pa r t o f t he c i r cu i t was done by t he Mic rocon t ro l l e r AT89C2051 . The

DTMF s igna l f r om the Te l ephone was decoded by t he Decode r IC

MT8870 . The Decode r ge t t he DTMF s igna l f r om Te l ephone l i ne and

t h i s decoded d ig i t a l s i gna l was f ed t o t he Mic rocon t ro l l e r . The

mic rocon t ro l l e r w i l l s en t t he decoded DTMF s igna l t o t he PC th rough

i t s s e r i a l po r t .

The da t a f rom the mic rocon t ro l l e r was f ed t o t he PC th rough a

vo l t age conve r t e r . The da t a f rom the compu te r s e r i a l po r t was i n

RS232 l og i c . Tha t i s f o r l og i c 1 t he vo l t age i s –9V and fo r l og i c 0 t he

vo l t age i s +9V and a t TTL s ide t he Vo l t age fo r l og i c 1 i s +5V and fo r

44

l og i c 0 i s 0V . The re fo r e fo r connec t i ng t h i s two s ec t i on (RS232 and

TTL) we need a conve r t e r .

The Conve r t e r u sed i n ou r c i r cu i t i s IC MAX232 . Th i s IC ha s

two s e t s o f conve r t e r i n wh ich we a r e u s ing a s e t . The da t a f rom the

PC i s f ed t o t he conve r t e r and t he conve r t e r conve r t s t he da t a i n to

TTL log i c wh ich i s f ed t o t he mic rocon t ro l l e r .

4 .1 .1 Te l ephone R ing s ensor

Th i s C i r cu i t c an be u sed t o connec t any t e l ephone t o t he t e l ephone

l i ne . When t he t e l ephone handse t s a r e i n on -hook pos i t i on , t he cu r r en t

t h rough t he op tocoup l e r LEDs i s i nadequa t e t o a c t i va t e t he i r i nbu i l t

t r an s i s t o r s . Howeve r t he r i ng s i gna l pa s se s t o t e l ephone i n pa r a l l e l

s i nce t he t e l ephone l i ne i s connec t ed t o t he t e l ephone i n s t rumen t s

t h rough combina t i on o f i nbu i l t LEDs o f op tocoup l e r s i n pa r a l l e l w i th

r eve r se d iodes wh i l e t he ‘ - ‘ma rked t e l ephone l i ne i s connec t ed t o t he

r e l ay . I n i t i a l l y when t he handse t s o f a l l t he t e l ephones a r e on t he

c r ad l e s , t he op tocoup l e r w i l l no t conduc t adequa t e ly and a s such t he

emi t t e r s o f i nbu i l t t r an s i s t o r s o f op tocoup l e r s a r e a t l ow l eve l . The

t r ans i s t o r ou tpu t ava i l ab l e a t t he emi t t e r s a r e i nve r t ed t o l og i c 1 s t a t e

and app l i ed t o t he Mic rocon t ro l l e r .

I n t h i s c i r cu i t op tocoup l e r i s u sed t o s ense t he r i ng s i gna l . A

r i ng vo l t age f rom exchange i s a round 70 t o 90vo l t ( 25 HZ AC) come

v i a t e l ephone l i ne s . The t e l ephone l i ne i s connec t ed t o t he r i ng s enso r

(op tocoup l e r IC MCT2E) w i l l de t ec t t h i s s i gna l and t he capac i t o r C2

(1µf /25v ) bypas se s t he 13 .5mA to60maA, AC r i ng ing cu r r en t so t ha t

t he op tocoup l e r ge t t u rned ON ( t he d iode an t i pa r a l l e l w i th t he LED)

an op tocoup l e r p rov ide cond i t i on du r ing t he nega t i ve ha l f cyc l e o f t he

r i ng ing cu r r en t . As t he r e su l t , t r an s i s t o r T1 ge t s f o rwa rd b i a sed and i t

conduc t s , pu l l i ng i t ’ s co l l e c to r t owards g round . Th i s w i l l t u rn ON the

45

r e l ay by p rov id ing t he magne t i z i ng cu r r en t . Th i s w i l l Cease s t he DC

vo l t age ac ros s t he phone l i ne . The aud io s i gna l i s ex t ended t o t he

ON/OFF hook de t ec to r (Op tocoup l e r IC ) . I f t he t e l ephone hand s e t i s

ON hook cond i t i on means t he t e l ephone L ine cons i s t o f 48v , t o ge t a

c l o sed l oop connec t i on w i th t he exchange f o r commun ica t i on . He re

an op tocoup l e r i s u sed fo r ON/OFF hook de t ec t i on , i t g e t s t h i s 48v a s

i npu t and t he pho tod iode acqu i r e a conduc t i on vo l t age a round 12v by

t he u se o f r e s i s t o r R1 . The conduc t i on o f pho tod iode emi t s l i gh t

t owards pho to t r ans i s t o r and t he r e by i t ge t s t he GND, wh ich connec t

a 10k r e s i s t o r (R2) a c ro s s t he Te l ephone L ine . So t ha t t he exchange

de t ec t a s i gna l f r om the subsc r i be r s , t ha t t he subsc r i be r was r eady fo r

commun ica t i on . I f t he t e l ephone l i ne i s u sed fo r message Tx and Rx

means , t he hand s e t i s f i r s t p i cked up t o con fo rm tha t t he i n coming

s i gna l i s Vo ice o r Message .Af t e r t ha t t he subsc r i be r c an p l ace t he

hand s e t w i th t he ba se s e t . Once t he hand s e t i s p i cked up means t he

µc w i l l s en t a a cknowledgemen t s i gna l t o t he µc a t t he de s igna t i on

s i de . so t ha t t he hook de t ec to r w i l l p rov ide vo l t age d rop i n t he Land

l i ne vo l t age , t he r e by a c l o sed l oop c i r cu i t i s f o rmed be tween

Subsc r i be r s and Te l ephone exchange .

I f i t i s a Vo ice s i gna l means t he ON/OFF hook de t ec to r f unc t i on

i s s ame and t he Hand s e t i s u sed fo r Vo ice commun ica t i on . Once t he

hand s e t i s p l a ced w i th t he ba se s e t a f t e r t he vo i ce o r message

commun ica t i on means t he Re l ay connec t ed w i th R ing s enso r ge t de -

ene rg i zed and Te l ephone l i ne i s d i s connec t ed by t he µc .

Optocoup ler ( IC MCT2E)

The MCT2E op to i so l a to r s cons i s t o f a ga l l i um a r sen ide i n f r a r ed

emi t t i ng d iode d r i v ing a s i l i con pho to t r ans i s t o r i n a 6 -p in dua l i n - l i ne

package .

46

F igu re .42 Pho to t r ans i s t o r Op tocoup l e

Feature

• UL r ecogn i zed (F i l e # E90700)

• VDE r ecogn i zed (F i l e # 94766)

• MCT2 and MCT2E a r e a l so ava i l ab l e i n wh i t e package

by spec i fy ing -M su f f i x , eg . MCT2-M

Schemat i c D iagram

F igu re .4 .3 Schema t i c d i ag ram o f op tocoup l e r

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PIN 1 . ANODE

2 . CATHODE

3. NO CONNECTION

4. EMITTER

5 . COLLECTOR

6. BASE

Appl i ca t ion

• Power supp ly r egu l a to r s

• D ig i t a l l og i c i npu t s

• Mic rop roces so r i npu t s

4 .1 .2 ON/OFF HOOK SIMULATOR

Dur ing r i ng s i gna l 70 t o 90V rms a t 20 -25HZ AC wi l l come

t h rough t he t e l ephone l i ne f rom the Exchange ba t t e ry . The ou tgo ing

s i gna l i ng r e f e r s s i gna l r e ach ing t he exchange f rom the subsc r i be r s

t e l ephone , i nd i ca t i ng ON-hook , OFF- hook , hang up , d i a l i ng e t c . Once

t he hand s e t i s p i cked up means i t i s i n o f f hook cond i t i on and now

the vo l t age r educes t o 47v t o 48v and ( i t i s g iven t o i npu t on ON/OFF

hook de t ec to r op tocoup l e r IC )Crad l e sw i t ch c lo se s t o fo rm a c lo sed

l oop c i r cu i t w i th t he exchange ba t t e ry and t he t e l ephone c i r cu i t . Th i s

c i r cu i t i s r e f e r r ed a s t he l oca l l oop c i r cu i t . Exchange ba t t e ry vo l t age s

a r e t yp i ca l l y 48 vo l t s . The l oop cu r r en t i s u sed by t he exchange t o

e s t ab l i sh ON/OFF hook s t a t u s o f t he t e l ephone . I f t he l oop cu r r en t i s

13 .5mA to 60mA the exchange de t ec t s i t a s OFF hook cond i t i on and i f

t he l oop cu r r en t i s l e s s t han 7 .5mA the exchange i n t e rp r e t s i t a s ON

hook cond i t i on .

48

The ope ra t ed l i ne vo l t age i s abou t 50v DC and t he i ncoming

vo i ce vo l t age t o t he t e l ephone i n s t rumen t va r i e s f rom 0 .5v t o 1 vo l t

and t he max imum ou t go ing vo i ce vo l t age i s abu t 2v rms .The r i ng

s i gna l i s 70 - 90v rms a t 20 -25HZ. In pu l s e d i a l i ng t e l ephones r eg i s t e r

s i gna l i ng i s known a s DC loop s i gna l i ng . I n t h i s c a se t he d i a l ed

number i s conveyed t o t he exchange by “make” and “b reak” o f l oop

c i r cu i t .

When a r i ng s i gna l i s p r e sen t , t he m ic rocon t ro l l e r w i l l sw i t ch on

t he RELAY to ach i eve OFF hook cond i t i on .

4 .1 .2 .1 RELAY

The r e l ay i s one o f t he mos t w ide ly u sed componen t s i n i ndus t r i a l

e l e c t ron i c s . I n combina t i on w i th t r ans i s t o r s , SCRs , e l e c t ron t ubes , and

o the r c i r cu i t e l emen t , t h i s e l e c t romagne t i c dev i ce pe r fo rms coun t l e s s

t a sks . Th i s r e l ays a r e u sed a s p ro t ec t i ve dev i ce fo r sw i t ch ing , f o r

i nd i ca t i ng and fo r t r ansmi s s ion .

T ransmi s s ion r e l ays a r e u sed i n con junc t i on w i th t r ans fo rmer s ,

i nduc to r s , c apac i t o r s i n power sy s t em and i n t e l ephone and i n o the r

commun ica t i on sy s t ems . Re l ays a r e e l e c t ro magne t i c a l l y ope ra t ed

r emo te ly con t ro l l ed sw i t ches w i th one o r more s e t s o f con t ac t s . When

ene rg i zed , t he r e l ay ope ra t e s t o open o r c l o se i t s con t ac t s o r t o open

some con t ac t s and c lo se o the r s . Con t ac t s wh ich a r e open when t he r e l ay

i s no t ene rg i zed a r e c a l l ed no rma l ly open (NO) o r s imp ly open

con t ac t s . Con t ac t s , wh i ch a r e c l o sed when t he r e l ay i s no t ene rg i zed ,

a r e c a l l ed no rma l ly c l o sed con t ac t s .

49

F igu re .4 .4 Re l ay

Re l ay con t ac t a r e he ld i n t he i r no rma l pos i t i on e i t he r by sp r i ng o r

by some g rav i t y a c t i va t ed mechan i sm . An ad ju s tmen t o r ad ju s tmen t s a r e

u sua l l y p rov ided t o s e t r e s t r a i n ing fo r ce t o c ause t he r e l ay t o ope ra t e

w i th in p r ede t e rmined c i r cu i t cond i t i ons .

Re l ays a r e e l e c t ro magne t i c componen t s wh ich ha s an ope ra t i ng

co i l and con t ac t . The co i l sha l l be ene rg i zed w i th AC o r DC supp ly .

Acco rd ing ly r e l ays a r e ava i l ab l e w i th AC\DC ope ra t i ng co i l s o f va r i ous

magn i t udes s ay f rom 6V DC to 220 V DC o r fo r AC vo l t age s r ang ing

f rom 20V AC to 440 AC.

The ope ra t i ng p r i nc ip l e o f r e l ays i s a s f o l l ows when t he co i l i s

ene rg i zed , an i r on co re a t t a ched t o t h i s a s semb ly ge t s magne t i z ed . Th i s

t hen a t t r a c t s an a rma tu re wh ich ha s e l e c t r i c a l connec t ed t o i t . The

e l e c t r i c a l t e rmina l s shou ld be f ab r i c a t ed i n such away t ha t t he r e sha l l be

one common t e rmina l ; one no rma l ly c l o sed (NC) con t ac t and one

no rma l ly open (NO) con t ac t s . When t he r e l ay i s no t ene rg i zed t he

connec t i on i s c l o sed be tween common and NO con t ac t s t h i s s t a t e i s

r eve r sed when t he r e l ay i s ene rg i zed t h i s r e l ay c i r cu i t sha l l be u sed t o

sw i t ch on o the r power c i r cu i t s , u s i ng l ow con t ro l vo l t age . The power

c i r cu i t and con t ro l c i r cu i t a r e p r ac t i c a l l y i so l a t ed .

50

Relay Cons truc t ion

A re l ay i s an e l e c t r i c a l l y con t ro l l ed dev i ce t ha t open and c lo se

e l e c t r i c a l con t ac t a f f ec t i ng o the r con t ac t s ( dev i ce s ) i n t he s ame o r o the r

c i r cu i t s . Ope ra t i on o f t he r e l ay i s d i s cus sed be low .

I f t he c i r cu i t i n t he co i l i s s l owly i nc r ea sed f rom 0 , a po in t w i l l be

r e ached whe re t he a rma tu re snaps ( c l o s ing t he gap ) and c lo se s t he

no rma l ly opened con t ac t (NO) .Th i s i s c a l l ed p i ckup po in t and i s

spec i f i ed by i t c i r cu i t o r vo l t age by t he manufac tu r e r when t he c i r cu i t i n

t he co i l i s g r adua l l y dec rea sed , a po in t we re t he f l ux i s t oo week t o ho ld

t he gap c lo sed i s r e ached and t he a rma tu re snaps open . Th i s i s c a l l ed t he

d ropou t c i r cu i t ( o r vo l t age ) and i s u sua l l y cons ide red l e s s t han t he

p i ckup cu r r en t ( o r vo l t age ) t he on ly no t i c eab l e phys i ca l d i f f e r ence

be tween AC and DC r e l ays w i th t he s ame r a t i ng i s t he add i t i on o f t he

shaded po l e a t t he end o f t he co re . A shaded po l e i s a conduc t i ng r i ng

t ha t c r ea t e s a magne t i c f i e l d t ha t l ay s t he app l i ed f i e l d , p roh ib i t i ng t he

r ap id co l l apse o f t he f l ux ac ros s t he gap . I f t h i s we re no t t he c a se t he

r e l ay wou ld hum o r cha t t e r a t a 60Hz r a t e and con t ac t pos i t i on wou ld be

unde t e rmined . The shad ing a l so cause s a r e r e l ays t o be i nhe ren t l y s l ower

t o r e l e a se t han dc r e l ays i f t he s ame s i z e . The de l ay i s abou t 100ms o r

l onge r t o p r even t con t ac t r e l e a se a t e ach po l a r i t y r eve r sa l on 60 Hz

ope ra t i on .

The con t ac t s i n an e l e c t romagne t i c r e l ays make o r b r eak t he

connec t i on i n e l e c t r i c c i r cu i t s h igh cu r r en t con t ac t s a r e u sua l l y o f t he

s i ng l e bu t t on o r by b i fu r ca t ed s t y l e . Nob l e me t a l a l l oys a r e u sed fo r t he

con t ac t ma t e r i a l t o r educe ox ida t i on t ha t c ause s ox ida t i on t ha t c ause s

h igh r e s i s t ance t he b i fu r ca t ed con t ac t ha s two su r f ace s fo r l e s s con t ac t

r e s i s t ance a t l owe r a c t i va t i ng fo r ce

51

The co re ba r con t ac t s a r e u sed fo r d ry c i r cu i t (NO o r l i t t l e cu r r en t

f l ow) and a r e made o f go ld t o h inde r and ox ida t i on fo r l ow l eve l (m i l l i

vo l t s o r m ic ro vo l t s ) Swi t ch ing c i r cu i t .

Con t ac t a r c ing i s more common in DC than i n AC c i r cu i t

i n t e r rup t i on t he AC c i r cu i t s go t h rough 0 vo l t age s a t e ach ha l f cyc l e and

ex t i ngu i sh any a r c ing t ha t occu r s . Any me ta l t r ans f e r i s gene ra l l y

e l im ina t ed , excep t f o r r oughen ing o f a con t ac t f a ce s . The DC a rc ing a r e

Spa rk d i s cha rge i s damag ing and w i l l c ause me t a l t o t r ans f e r f rom the

nega t i ve con t ac t t o t he pos i t i ve con t ac t .

4 .1 .3 Ser ia l Por t s in Computer

Al l IBM PC and compa t i b l e compu te r s a r e t yp i ca l l y equ ipped

w i th two se r i a l po r t s and one pa ra l l e l po r t . A l t hough t he se two t ypes

o f po r t s a r e u sed fo r commun ica t i ng w i th ex t e rna l dev i ce s , t hey work

i n d i f f e r en t ways .

A pa ra l l e l po r t s ends and r ece ive s da t a e i gh t b i t s a t a t ime ove r

8 s epa ra t e w i r e s . Th i s a l l ows da t a t o be t r ans f e r r ed ve ry qu i ck ly ;

howeve r , t he c ab l e r equ i r ed i s more bu lky because o f t he number o f

i nd iv idua l w i r e s i t mus t con t a in . Pa r a l l e l po r t s a r e t yp i ca l l y u sed t o

connec t a PC to a p r i n t e r and a r e r a r e ly u sed fo r much e l s e . A s e r i a l

po r t s ends and r ece ive s da t a one b i t a t a t ime ove r one w i r e . Whi l e i t

t ake s e i gh t t imes a s l ong t o t r ans f e r e ach by t e o f da t a t h i s way , on ly a

f ew wi r e s a r e r equ i r ed . I n f a c t , two-way ( fu l l dup l ex ) commun ica t i ons

i s pos s ib l e w i th on ly t h r ee s epa ra t e w i r e s - one t o s end , one t o

r e ce ive , and a common s igna l g round w i r e .

52

In troduc t ion to Ser ia l Por t

The UART se r i a l po r t ( o r j u s t " s e r i a l po r t f o r sho r t " i s an I /O

( Inpu t /Ou tpu t ) dev i ce . An I /O dev i ce i s j u s t a way t o ge t da t a i n to and

ou t o f a compu te r . The re a r e many t ypes o f I /O dev i ce s such a s s e r i a l

po r t s , pa r a l l e l po r t s , d i sk d r i ve con t ro l l e r s , e t he rne t boa rds , un ive r sa l

s e r i a l buse s , e t c . Mos t PC ' s have one o r two s e r i a l po r t s . Each ha s a

9 -p in connec to r ( some t imes 25 -p in ) on t he back o f t he compu te r .

Compu te r p rog rams can s end da t a (by t e s ) t o t he t r ansmi t p in (ou tpu t )

and r ece ive by t e s f rom the r e ce ive p in ( i npu t ) . The o the r p in s a r e fo r

con t ro l pu rpose s and g round .

The s e r i a l po r t i s much more t han j u s t a connec to r . I t conve r t s

t he da t a f rom pa ra l l e l t o s e r i a l and changes t he e l e c t r i c a l

r ep re sen t a t i on o f t he da t a . I n s ide t he compu te r , da t a b i t s f l ow in

pa r a l l e l ( u s ing many w i r e s a t t he s ame t ime ) . Se r i a l f l ow i s a s t r e am

o f b i t s ove r a s i ng l e w i r e ( such a s on t he t r ansmi t o r r e ce ive p in o f

t he s e r i a l connec to r ) . Fo r t he s e r i a l po r t t o c r ea t e such a f l ow , i t mus t

conve r t da t a f rom pa ra l l e l ( i n s ide t he compu te r ) t o s e r i a l on t he

t r ansmi t p in ( and conve r se ly ) .

Pins and Wires

Old PC ' s u sed 25 p in connec to r s bu t on ly abou t 9 p in s we re

ac tua l l y u sed so t oday mos t connec to r s a r e on ly 9 -p in . Each o f t he 9

p in s u sua l l y connec t s t o a w i r e . Bes ide s t he two wi r e s u sed fo r

t r ansmi t t i ng and r ece iv ing da t a , ano the r p in (w i r e ) i s s i gna l g round .

The vo l t age on any w i r e i s measu red w i th r e spec t t o t h i s g round .

53

Thus t he min imum number o f w i r e s t o u se fo r 2 -way

t r ansmi s s ion o f da t a i s 3 . Excep t t ha t i t h a s been known to work w i th

no s i gna l g round w i r e bu t w i th deg raded pe r fo rmance and some t imes

w i th e r ro r s . The re a r e s t i l l more w i r e s wh ich a r e fo r con t ro l pu rpose s

( s i gna l i ng ) on ly and no t f o r s end ing by t e s . A l l o f t he se s i gna l s cou ld

have been sha red on a s i ng l e w i r e , bu t i n s t e ad , t he r e i s a s epa ra t e

ded i ca t ed w i r e fo r eve ry t ype o f s i gna l . Some (o r a l l ) o f t he se con t ro l

w i r e s a r e c a l l ed "modem con t ro l l i ne s " . Modem con t ro l w i r e s a r e

e i t he r i n t he a s se r t ed s t a t e ( on ) o f +12 vo l t s o r i n t he nega t ed s t a t e

( o f f ) o f - 12 vo l t s . One o f t he se w i r e s i s t o s i gna l t he compu te r t o s t op

s end ing by t e s ou t t he s e r i a l po r t c ab l e . Conve r se ly , ano the r w i r e

s i gna l s t he dev i ce a t t a ched t o t he s e r i a l po r t t o s t op s end ing by t e s t o

t he compu te r . I f t he a t t a ched dev i ce i s a modem, o the r w i r e s may t e l l

t he modem to hang up t he t e l ephone l i ne o r t e l l t he compu te r t ha t a

connec t i on ha s been made o r t ha t t he t e l ephone l i ne i s r i ng ing

( someone i s a t t emp t ing t o c a l l i n ) .

Bi -Direc t i ona l Communica t ions

The s e r i a l po r t on you r PC i s a f u l l - dup l ex dev i ce mean ing t ha t

i t c an s end and r ece ive da t a a t t he s ame t ime . I n o rde r t o be ab l e t o

do t h i s , i t u se s s epa ra t e l i ne s fo r t r ansmi t t i ng and r ece iv ing da t a .

Some types o f s e r i a l dev i ce s suppo r t on ly one -way commun ica t i ons

and t he r e fo re u se on ly two wi r e s i n t he c ab l e - t he t r ansmi t l i ne and

t he s igna l g round .

Communica t ing By B i t s

Once t he s t a r t b i t ha s been s en t , t he t r ansmi t t e r s ends t he a c tua l

da t a b i t s . The re may e i t he r be 5 , 6 , 7 , o r 8 da t a b i t s , depend ing on t he

number you have s e l ec t ed . Bo th r ece ive r and t he t r ansmi t t e r mus t

54

ag ree on t he number o f da t a b i t s , a s we l l a s t he baud r a t e . A lmos t a l l

dev i ce s t r ansmi t da t a u s ing e i t he r 7 o r 8 da t a b i t s . No t i c e t ha t when

on ly 7 da t a b i t s a r e emp loyed , you canno t s end ASCI I va lue s g r ea t e r

t han 127 . L ikewi se , u s ing 5 b i t s l im i t s t he h ighes t pos s ib l e va lue t o

31 . Af t e r t he da t a ha s been t r ansmi t t ed , a s t op b i t i s s en t . A s t op b i t

ha s a va lue o f 1 - o r a ma rk s t a t e - and i t c an be de t ec t ed co r r ec t l y

even i f t he p r ev ious da t a b i t a l so had a va lue o f 1 . Th i s i s

a ccompl i shed by t he s t op b i t ' s du ra t i on . S top b i t s c an be 1 , 1 . 5 , o r 2

b i t pe r i ods i n l eng th .

The Par i ty B i t

Bes ide s t he synch ron i za t i on p rov ided by t he u se o f s t a r t and

s t op b i t s , an add i t i ona l b i t c a l l ed a pa r i t y b i t may op t i ona l l y be

t r ansmi t t ed a long w i th t he da t a . A pa r i t y b i t a f fo rds a sma l l amoun t

o f e r ro r check ing , t o he lp de t ec t da t a co r rup t i on t ha t m igh t occu r

du r ing t r ansmi s s ion . You can choose even pa r i t y , odd pa r i t y , ma rk

pa r i t y , space pa r i t y o r none a t a l l . When even o r odd pa r i t y i s be ing

u sed , t he number o f ma rks ( l og i ca l 1 b i t s ) i n e ach da t a by t e i s

coun t ed , and a s i ng l e b i t i s t r ansmi t t ed fo l l owing t he da t a b i t s t o

i nd i ca t e whe the r t he number o f 1 b i t s j u s t s en t i s even o r odd .

Fo r example , when even pa r i t y i s chosen , t he pa r i t y b i t i s

t r ansmi t t ed w i th a va lue o f 0 i f t he number o f p r eced ing marks i s an

even number . Fo r t he b ina ry va lue o f 0110 0011 t he pa r i t y b i t wou ld

be 0 . I f even pa r i t y was i n e f f ec t and t he b ina ry number 1101 0110

was s en t , t hen t he pa r i t y b i t wou ld be 1 . Odd pa r i t y i s j u s t t he

oppos i t e , and t he pa r i t y b i t i s 0 when t he number o f ma rk b i t s i n t he

p r eced ing word i s an odd number . Pa r i t y e r ro r check ing i s ve ry

rud imen ta ry . Whi l e i t w i l l t e l l you i f t he r e i s a s i ng l e b i t e r ro r i n t he

cha rac t e r , i t doe sn ' t show wh ich b i t was r e ce ived i n e r ro r . A l so , i f

55

even number s o f b i t s a r e i n e r ro r t hen t he pa r i t y b i t wou ld no t r e f l e c t

any e r ro r a t a l l .

Mark pa r i t y means t ha t t he pa r i t y b i t i s a lways s e t t o t he ma rk

s i gna l cond i t i on and l i kewi se space pa r i t y a lways s ends t he pa r i t y b i t

i n t he space s i gna l cond i t i on . S ince t he se two pa r i t y op t i ons s e rve no

u se fu l pu rpose wha t soeve r , t hey a r e a lmos t neve r u sed .

RS-232C

RS-232 s t ands fo r Recommend S t anda rd number 232 and C i s

t he l a t e s t r ev i s i on o f t he s t anda rd . The s e r i a l po r t s on mos t compu te r s

u se a subse t o f t he RS-232C s t anda rd . The fu l l RS-232C s t anda rd

spec i f i e s a 25 -p in "D" connec to r o f wh ich 22 p in s a r e u sed . Mos t o f

t he se p in s a r e no t needed fo r no rma l PC commun ica t i ons , and i ndeed ,

mos t new PCs a r e equ ipped w i th ma l e D t ype connec to r s hav ing on ly

9 p in s .

Pin De ta i l s o f PC Ser ia l por t

RICTSRTSDSR

GNDDTRTDRDCD

RS232Connector

67895

4321

56

9 P in Connec tor on a DTE dev i ce (PC connec t ion )

P in

NumberDirec t i on o f s i gna l :

1Car r i e r De t ec t (CD) ( f rom DCE) Incoming s i gna l f r om a

modem

2 Rece ived Da t a (RD) Incoming Da t a f rom a DCE

3 Transmi t t ed Da t a (TD) Ou tgo ing Da t a t o a DCE

4 Da ta Te rmina l Ready (DTR) Ou tgo ing handshak ing s i gna l

5 S igna l Ground Common r e f e r ence vo l t age

6 Da ta Se t Ready (DSR) Incoming handshak ing s i gna l

7 Reques t To Send (RTS) Ou tgo ing f l ow con t ro l s i gna l

8 C lea r To Send (CTS) Incoming f l ow con t ro l s i gna l

9R ing Ind i ca to r (R I ) ( f rom DCE) Incoming s i gna l f r om a

modem

Tab l e 4 .1 : P in s o f RS232

The TD ( t r ansmi t da t a ) w i r e i s t he one t h rough wh ich da t a f rom

a DTE dev i ce i s t r ansmi t t ed t o a DCE dev i ce . Th i s name can be

dece iv ing , because t h i s w i r e i s u sed by a DCE dev i ce t o r e ce ive i t s

da t a . The TD l i ne i s kep t i n a ma rk cond i t i on by t he DTE dev i ce when

i t i s i d l e . The RD ( r ece ive da t a ) w i r e i s t he one on wh ich da t a i s

r e ce ived by a DTE dev i ce . RTS s t ands fo r Reques t To Send . Th i s l i ne

and t he CTS l i ne a r e u sed when "ha rdware f l ow con t ro l " i s enab l ed i n

bo th t he DTE and DCE dev i ce s .

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The DTE dev i ce pu t s t h i s l i ne i n a ma rk cond i t i on t o t e l l t he

r emo te dev i ce t ha t i t i s r e ady and ab l e t o r e ce ive da t a . I f t he DTE

dev i ce i s no t ab l e t o r e ce ive da t a ( t yp i ca l l y because i t s r e ce ive bu f f e r

i s a lmos t f u l l ) , i t w i l l pu t t h i s l i ne i n t he space cond i t i on a s a s i gna l

t o t he DCE to s t op s end ing da t a . When t he DTE dev i ce i s r e ady t o

r e ce ive more da t a ( i . e . a f t e r da t a ha s been r emoved f rom i t ’ s r e ce ive

bu f f e r ) , i t w i l l p l a ce t h i s l i ne back i n t he ma rk cond i t i on . The

complemen t o f t he RTS wi r e i s CTS , wh ich s t ands fo r C l ea r t o Send .

The DCE dev i ce pu t s t h i s l i ne i n a ma rk cond i t i on t o t e l l t he DTE

dev i ce t ha t i t i s r e ady t o r e ce ive t he da t a .

L ikewi se , i f t he DCE dev i ce i s unab l e t o r e ce ive da t a , i t w i l l

p l a ce t h i s l i ne i n t he space cond i t i on . Toge the r , t he se two l i ne s make

up wha t i s c a l l ed RTS/CTS o r "ha rdware" f l ow con t ro l . The So f twa re

Wedge suppo r t s t h i s t ype o f f l ow con t ro l , a s we l l a s Xon /XOf f o r

" so f twa re" f l ow con t ro l . So f twa re f l ow con t ro l u se s spec i a l con t ro l

cha rac t e r s t r ansmi t t ed f rom one dev i ce t o ano the r t o t e l l t he o the r

dev i ce t o s t op o r s t a r t s end ing da t a . Wi th so f twa re f l ow con t ro l t he

RTS and CTS l i ne s a r e no t u sed .

DTR s t ands fo r Data Termina l Ready . I t s i n t ended func t i on i s

ve ry s im i l a r t o t he RTS l i ne . DSR (Da t a Se t Ready ) i s t he compan ion

t o DTR in t he s ame way t ha t CTS i s t o RTS . Some se r i a l dev i ce s u se

DTR and DSR a s s i gna l s t o s imp ly con f i rm tha t a dev i ce i s connec t ed

and i s t u rned on . The So f twa re Wedge s e t s DTR to t he ma rk s t a t e

when t he s e r i a l po r t i s opened and l e aves i t i n t ha t s t a t e un t i l t he po r t

i s c l o sed . The DTR and DSR l i ne s we re o r i g ina l l y de s igned t o p rov ide

an a l t e rna t e me thod o f ha rdware handshak ing . I t wou ld be po in t l e s s t o

u se bo th RTS/CTS and DTR/DSR fo r f l ow con t ro l s i gna l s a t t he s ame

t ime . Because o f t h i s , DTR and DSR a re r a r e ly u sed fo r f l ow con t ro l .

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CD s t ands fo r Carr i er De tec t . Ca r r i e r De t ec t i s u sed by a

modem to s i gna l t ha t i t h a s a made a connec t i on w i th ano the r modem,

o r ha s de t ec t ed a c a r r i e r t one .

The l a s t r ema in ing l i ne i s RI o r Ring Ind ica tor . A modem

togg l e s t he s t a t e o f t h i s l i ne when an i ncoming ca l l r i ngs you r phone .

The Ca r r i e r De t ec t (CD) and t he R ing Ind i ca to r (R I ) l i ne s a r e

on ly ava i l ab l e i n connec t i ons t o a modem. Because mos t modems

t r ansmi t s t a t u s i n fo rma t ion t o a PC when e i t he r a c a r r i e r s i gna l i s

de t ec t ed ( i . e . when a connec t i on i s made t o ano the r modem) o r when

t he l i ne i s r i ng ing , t he se two l i ne s a r e r a r e ly u sed .

4 .2 POWER SUPPLY

F igu re 45 Power Supp ly Un i t

The power supp ly s ec t i on i s t he impor t an t one . I t shou ld de l i ve r

cons t an t ou tpu t r egu l a t ed power supp ly fo r succe s s fu l work ing o f t he

p ro j ec t . A 0 -12V/500mA t r ans fo rmer i s u sed fo r ou r pu rpose ; t he

59

pr imary o f t h i s t r ans fo rmer i s connec t ed i n t o ma in supp ly t h rough

on /o f f sw i t ch& fuse fo r p ro t ec t i ng f rom ove r load and sho r t c i r cu i t

p ro t ec t i on . The s econda ry i s connec t ed t o t he d iodes conve r t f r om

12V AC to 12V DC vo l t age , wh ich i s f u r t he r r egu l a t ed t o +5v , by

u s ing IC 7805 .

4 .2 .1 Regu la tor IC (LM 7805)

The LM7805 mono l i t h i c 3 - t e rmina l pos i t i ve vo l t age r egu l a to r s

emp loy i n t e rna l cu r r en t - l im i t i ng , t he rma l shu tdown and s a f e - a r ea

compensa t i on , mak ing t hem e s sen t i a l l y i ndes t ruc t i b l e . I f adequa t e

hea t s i nk ing i s p rov ided , t hey can de l i ve r ove r 1 .0A ou tpu t cu r r en t .

They a r e i n t ended a s f i xed vo l t age r egu l a to r s i n a w ide r ange o f

app l i c a t i ons i nc lud ing l oca l ( on -ca rd ) r egu l a t i on fo r e l im ina t i on o f

no i s e and d i s t r i bu t i on p rob l ems a s soc i a t ed w i th s i ng l e -po in t

r egu l a t i on . I n add i t i on t o u se a s f i xed vo l t age r egu l a to r s , t he se

dev i ce s c an be u sed w i th ex t e rna l componen t s t o ob t a in ad ju s t ab l e

ou tpu t vo l t age s and cu r r en t s .

Cons ide rab l e e f fo r t was expended t o make t he en t i r e s e r i e s o f

r egu l a to r s e a sy t o u se and min imize t he number o f ex t e rna l

componen t s . I t i s no t nece s sa ry t o bypas s t he ou tpu t , a l t hough t h i s

does improve t r ans i en t r e sponse . I npu t bypas s ing i s needed on ly i f t he

r egu l a to r i s l oca t ed f a r f r om the f i l t e r c apac i t o r o f t he power supp ly .

F igu re .4 .6 P in s o f LM780

60

5 . SOFTWARE DESCRIPTION

5.1 V i sua l Bas i c 6 .0

Visua l Bas i c (V i sua l Beg inne r s A l l pu rpose symbo l i c

In s t ruc t i on Code ) i s t he mos t popu l a r p rog ramming l anguage fo r

wor ld ’ s mos t popu l a r ope ra t i ng sy s t em. V i sua l Bas i c i s t he f i r s t

l anguage peop l e cons ide r when t hey wan t r ap id app l i c a t i on

deve lopmen t fo r t he w indow env i ronmen t . V i sua l Bas i c i s evo lved

f rom the o r i g ina l BASIC l anguage , wh ich i s w ide ly u sed l anguage .

Ex i s t i ng ob j ec t s a r e d r agged & d ropped i n t o t he p l ace i n s t e ad o f

wr i t i ng numerous codes . Whi l e wr i t i ng t he p rog rams , we a r e ab l e t o

s ee how the p rog rams run du r ing t he run t ime . Th i s i s g r ea t advan t age

ove r o the r p rog ramming l anguage . VB i s ba sed on an even t d r i ven

me thod mode l ; i t a l so ha s a s e t o f debugg ing t oo l s . The p r ima ry

r ea son beh ind s e l ec t i ng VB was because t he i n t e r f ace was so l i t t l e

compa red t o o the r t oo l s .

Proper t i e s

The p rope r t i e s de sc r i be t he appea rance o f t he GUI componen t .

When add ing a componen t , t he Name p rope r ty shou ld be s e t

immed ia t e ly , a cco rd ing t o t he t h r ee - l e t t e r mnemon ic naming

conven t i ons . The p rope r t i e s a r e d i sp l ayed i n t he P rope r t i e s Window in

Name /Va lue pa i r s i n a l phabe t i c a l o rde r .

Event Procedures

An even t p rocedu re i s a p i ece o f code t ha t r e sponds t o even t s

t ha t c an occu r fo r t ha t ob j ec t . Mos t o f t he even t s a r e gene ra t ed by t he

u se r , enab l i ng t hem to d i c t a t e t he o rde r o f execu t i on .

61

Forms

The Fo rm i s t he ma in s t age o f you r app l i c a t i on . By de fau l t , t he

S t anda rd Exe op t i on s t a r t s w i th a f o rm ca l l ed "Fo rm1" . The Name

p rope r ty o f t he Fo rm shou ld be named wi th a t h r ee - l e t t e r mnemon ic

p r e f i x o f " f rm" . Each Fo rm wi l l be a Window in you r app l i c a t i on .

Con t ro l s a r e added t o t he fo rm by e i t he r doub l e - c l i ck ing t hem in t he

t oo lbox , o r by s e l ec t i ng t he con t ro l and d r awing a bound ing r ec t ang l e

on t he fo rm . Your app l i c a t i on may use more t han one fo rm .

To add a new Fo rm to t he p ro j ec t , e i t he r s e l e c t "Add Fo rm"

f rom the "P ro j ec t " menu o r r i gh t - c l i ck t he Fo rms fo lde r i n t he P ro j ec t

Exp lo re r and s e l ec t , "Add" , and t hen "Fo rm" .

To l oad a new fo rm , u se t he Show me thod . The pa rame te r ,

vbModa l , i s op t i ona l . I f u sed , vbModa l means t ha t t he fo rm has focus

un t i l c l o sed w i th in t he app l i c a t i on .

The Load command can be u sed t o l oad a fo rm wi thou t showing

i t . Th i s t e chn ique i s u se fu l i f you wan t t o p r e load a fo rm , and t hen

u se e i t he r t he "Show" o r "V i s ib l e " me thod t o make i t v i s i b l e a s and

when r equ i r ed .

No te : I n VB.Ne t , t he r e a r e two t ypes o f Fo rms - Windows Fo rms and

Web Fo rms . Web Fo rms a r e ba sed on ASP .Ne t .

62

Standard Contro l s

Con t ro l s a r e added t o t he Fo rm f rom the Too lbox . Each con t ro l

ha s a s e t o f p rope r t i e s , and a s e t o f even t p rocedu re s a s soc i a t ed w i th

i t . The fo l l owing l i s t s t he con t ro l , r e ad ing l e f t t o r i gh t , t op t o bo t t om

a s t hey appea r i n t he s t anda rd Too lbox .

The Po in ter

The Po in t e r i s no t a con t ro l , bu t i s u sed t o i n t e r ac t w i th t he

con t ro l s on t he fo rm , a l l owing you t o move and r e s i z e t hem. The

Po in t e r i s s e l e c t ed by de fau l t . When a con t ro l i s added t o t he fo rm ,

t he focus r eve r t s back t o t he Po in t e r .

Pic tureBox Contro l

The P i c tu r eBox i s u sed t o d i sp l ay images o r a c t a s a con t a ine r

t o o the r con t ro l s . The t h r ee - l e t t e r mnemon ic fo r a P i c tu r eBox i s p i c

( eg . p i cFace ) . The ma in even t f o r a P i c tu r eBox i s t he C l i ck even t .

P i c tu r e s a r e l oaded i n to t he P i c tu r eBox us ing t he LoadP ic tu r e

func t i on . The fo l l owing example t ogg l e s be tween f ace0 .g i f and

f ace1 .g i f w i th e ach c l i ck o f t he mouse .

Labe l Contro l

The Labe l con t ro l i s u sed t o d i sp l ay t ex t t ha t c an ' t be changed

d i r ec t l y by t he u se r . Labe l s a r e more common ly u sed t o p l ace cap t i ons

aga in s t o the r con t ro l s o r s t o r e c a l cu l a t ed va lue s . The t h r ee - l e t t e r

mnemon ic fo r a Labe l i s l b l ( eg . l b lP rompt ) .

The de fau l t p rope r ty o f a Labe l i s Cap t i on . The Cap t i on p rope r ty may

be s e t a t de s ign - t ime u s ing t he P rope r t i e s Window, and changed a t

r un - t ime .

63

Labe l Contro l

The Labe l con t ro l i s u sed t o d i sp l ay t ex t t ha t c an ' t be changed

d i r ec t l y by t he u se r . Labe l s a r e more common ly u sed t o p l ace cap t i ons

aga in s t o the r con t ro l s o r s t o r e c a l cu l a t ed va lue s . The t h r ee - l e t t e r

mnemon ic fo r a Labe l i s l b l ( eg . l b lP rompt ) . The de fau l t p rope r ty o f a

Labe l i s Cap t i on . The Cap t i on p rope r ty may be s e t a t de s ign - t ime

u s ing t he P rope r t i e s Window, and changed a t r un - t ime .

To a l l ow t ex t on more t han one l i ne , t he Mul t i l i ne P rope r ty

mus t be s e t t o T rue . I f t he Sc ro l lBa r s P rope r ty doesn ' t a l l ow a

Hor i zon t a l Sc ro l lBa r , t hen t he t ex t w i l l wrap . The l eng th o f t he Tex t

p rope r ty i s l im i t ed t o 2048 cha rac t e r s f o r a Tex tBox , and abou t 32K i f

t he Mul t iL ine p rope r ty i s s e t t o T rue .

Frame Contro l

The F rame con t ro l i s u sed t o g roup con t ro l s and p rov ide s a

means o f sub -d iv id ing t he Fo rm v i sua l l y . The t h r ee - l e t t e r mnemon ic

fo r a F rame i s f r a ( eg . f r aPaymen tMe thod ) . The de fau l t p rope r ty i s

Cap t i on , wh ich can be u sed t o g ive con t ex t t o t he g roup ing ( eg .

Paymen t Me thod ) .

When op t i on bu t t ons a r e u sed , on ly one may be s e l ec t ed on t he

Fo rm. Op t ion Bu t tons p l aced i n a F rame a r e a s soc i a t ed w i th t he

F rame , and a r e t r e a t ed a s a new g roup .

Command But ton Contro l

The Command Bu t ton i s u sed by t he u se r t o i nvoke some ac t i on .

The t h r ee - l e t t e r mnemon ic fo r a Command Bu t ton i s cmd ( eg .

cmdQui t ) . The de fau l t even t f o r a Command Bu t ton i s "C l i ck" .

64

Checkbox Contro l

The CheckBox con t ro l i s u sed t o g ive t he u se r a cho i ce o f

ye s /no mu l t i p l e cho i ce op t i ons . The t h r ee - l e t t e r mnemon ic fo r a

CheckBox i s chk ( eg . chkHobb ie s ) . The "Va lue" p rope r ty may be u sed

t o de t e rmine whe the r an i t em has been s e l ec t ed - a va lue o f 1

i nd i ca t e s t r ue , and a va lue o f 0 i nd i ca t e s f a l s e . The fo l l owing

example u se s a command bu t t on t o de t e rmine wh ich i t ems have been

s e l ec t ed f rom a con t ro l a r r ay o f CheckBoxes .

Opt ionBut ton Contro l

The Op t ionBu t ton con t ro l i s u sed t o g roup op t i ons whe re t he

u se r c an on ly s e l ec t on ly one . As on ly one i t em may be s e l ec t ed

Op t ionBu t tons a r e g rouped i n con t a ine r s such a s t he Fo rm, F rame o r

P i c tu r eBox . The t h r ee - l e t t e r mnemon ic fo r an Op t ionBu t ton i s op t ( eg .

op tPaymen tMe thod ) . The "Va lue" p rope r ty may be u sed t o de t e rmine

whe the r an i t em has been s e l ec t ed - e i t he r T rue o r Fa l s e . The

fo l l owing example u se s a CommandBu t ton t o de t e rmine wh ich i t em

has been s e l ec t ed f rom a con t ro l a r r ay o f Op t ionBu t tons .

ComboBox Contro l

The ComboBox i s a combina t i on o f a Tex tBox and a L i s tBox

con t ro l . I t ems may be added t o t he l i s t a t de s ign - t ime u s ing t he "L i s t "

p rope r ty (<CTRL>+<ENTER> t akes you t o t he nex t l i ne t o add a new

i t em) . I t ems may be added t o t he l i s t a t r un - t ime u s ing t he AddI t em

me thod , and r emoved a t r un - t ime u s ing t he Remove I t em me thod ( s ee

be low fo r de t a i l s ) . The "C lea r " me thod r emoves a l l i t ems f rom the

l i s t . The t h r ee - l e t t e r mnemon ic fo r a ComboBox i s cbo ( eg .

cboAr t i s t ) .

65

Timer Contro l

The T imer con t ro l i s v i s i b l e a t de s ign - t ime , bu t no t shown a t

r un - t ime . I t i s u sed fo r backg round p roce s s ing a t i n t e rva l s spec i f i ed

by t he In t e rva l p rope r ty . The In t e rva l p rope r ty t ake s an i n t ege r i n t he

r ange 0 t o 65 ,535 . The In t e rva l i s measu red i n m i l l i s econds ; t he r e fo re

a va lue o f 1000 equa l s an i n t e rva l o f one s econd . An In t e rva l o f 0

d i s ab l e s t he T imer con t ro l i n VB 6 , bu t no t i n VB.Ne t . To d i s ab l e t he

T imer , s e t t he Enab l ed P rope r ty t o Fa l s e . Se t t i ng i t t o T rue w i l l

enab l e i t aga in . The t h r ee - l e t t e r mnemon ic fo r a T imer i s tmr ( eg .

tmrMove ) . The de fau l t even t f o r a T imer i s t he T imer even t .

Th i s example moves a P i c tu r eBox a round t he fo rm . To t ry t he

example , add a P i c tu r eBox ca l l ed p i cFace , and a T imer c a l l ed

tmrMove t o t he fo rm . Se t t he In t e rva l o f t he T imer t o 1 , and add a

p i c tu r e o f a f a ce t o t he P i c tu r eBox .

5 .2 . V i sua l Bas i c (Ser ia l Communica t ion )

5 .2 .1 In troduc t ion

Thi s chap t e r d i s cus se s how Vi sua l Bas i c c an be u sed t o a cce s s

s e r i a l commun ica t i on func t i ons . Windows h ide s much o f t he

complex i t y o f s e r i a l commun ica t i ons and au toma t i ca l l y pu t s any

r ece ived cha rac t e r s i n a r e ce ive bu f f e r and cha rac t e r s s en t i n to a

t r ansmi s s ion bu f f e r . The r ece ive bu f f e r c an be r ead by t he p rog ram

wheneve r i t ha s t ime and t he t r ansmi t bu f f e r i s emp t i ed when i t i s

f r e e t o s end cha rac t e r s .

5 .2 .2 Communica t ions contro l

Visua l Bas i c a l l ows many add i t i ona l componen t s t o be added t o

t he t oo lbox . The Mic roso f t Comm. componen t i s u sed t o add a s e r i a l

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communica t i on f ac i l i t y . I n o rde r t o u se t he Comms componen t t he

f i l e s MSCOMM16.OCX ( fo r a 16 -b i t modu le ) o r MSCOMM32.OCX

( fo r a 32 -b i t modu le ) mus t be p r e sen t i n t he \WINDOWS\SYSTEM

d i r ec to ry . The c l a s s name i s MSComm. The commun ica t i ons con t ro l

p rov ide s t he fo l l owing two ways fo r hand l i ng commun ica t i ons

Event -dr iven

Even t -d r i ven commun ica t i ons i s t he be s t me thod o f hand l i ng

s e r i a l commun ica t i on a s i t f r e e s t he compu te r t o do o the r t h ings . The

even t c an be de f i ned a s t he r e cep t i on o f a cha rac t e r , a change i n CD

( ca r r i e r de t ec t ) o r a change i n RTS ( r eques t t o s end ) . The OnComm

even t c an be u sed t o c ap tu r e t he se even t s . and a l so t o de t ec t

commun ica t i ons e r ro r s .

Pol l ing

CommEven t p rope r t i e s c an be t e s t ed t o de t e rmine i f an even t o r

an e r ro r ha s occu r r ed . Fo r example , t he p rog ram can l oop wa i t i ng fo r

a cha rac t e r t o be r e ce ived . Once i t i s t he cha rac t e r i s r e ad f rom the

r e ce ive bu f f e r . Th i s me thod i s no rma l ly u sed when t he p rog ram has

t ime t o po l l t he commun ica t i ons r e ce ive r o r t ha t a known r e sponse i s

imminen t .

V i sua l Bas i c u se s t he s t anda rd Windows d r i ve r s f o r t he s e r i a l

commun ica t i on po r t s ( such a s s e r i a l u i . d l l and s e r i a l . vxd ) . The

commun ica t i on con t ro l i s added t o t he app l i c a t i on fo r e ach po r t . The

pa rame te r s ( such a s t he b i t r a t e , pa r i t y , and so on ) c an be changed by

s e l ec t i ng Con t ro l Pane l ? Sys t em ? Dev i ce Manage r ? Po r t s (COM

and LPT) ? Po r t Se t t i ngs . The s e t t i ngs o f t he commun ica t i ons po r t

( t he IRQ and t he po r t add re s s ) c an be changed by s e l ec t i ng Con t ro l

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Pane l ? Sys t em? Dev i ce Manage r? Po r t s (COM and LPT)? Resou rce s

fo r IRQ and Addre s se s .

Proper t i e s

The Comm componen t i s added t o a f o rm wheneve r s e r i a l

commun ica t i ons a r e r equ i r ed . By de fau l t , t he f i r s t c r ea t ed ob j ec t i s

named MSComm1 ( t he s econd i s named MSComm2, and so on ) . I t c an

be s een t ha t t he ma in p rope r t i e s o f t he ob j ec t a r e : CommPor t ,

DTREnab l e , EOFEnab l e , Handshak ing , I nBuf f e rS i ze , I ndex , I npu tLen ,

I npu tMode , Le f t , Name , Nu l lD i sca rd , Ou tBuf f e rS i ze , Pa r i t yRep l ace ,

RThre sho ld , RTSEnab l e , Se t t i ngs , SThre sho ld , Tag and Top .

Se t t ings

The Se t t i ngs p rope r ty s e t s and r e tu rns t he RS-232 pa rame te r s ,

such a s baud r a t e , pa r i t y , t he number o f da t a b i t , and t he number o f

s t op b i t s . I t s syn t ax i s :

[ f o rm . ]MSComm. Se t t i ngs = s e tS t r [$]

where t he s t rS t r i s a s t r i ng wh ich con t a in s t he RS-232 s e t t i ngs . Th i s

s t r i ng t ake s t he fo rm:

"BBBB,P ,D ,S"

whe re

BBBB def ine s t he baud r a t e ,

P t he pa r i t y ,

D t he number o f da t a b i t s , and

S t he number o f s t op b i t s .

The fo l l owing l i s t s t he va l i d baud r a t e s ( de f au l t i s 9600Baud) :

110 , 300 , 600 , 1200 , 2400 , 9600 , 14400 , 19200 , 38400 , 56000 ,

128000 , 256000 .

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The va l i d pa r i t y va lue s a r e (de f au l t i s N) : E (Even ) , M (Mark ) , N

(None ) , O (Odd) , S (Space ) .

The va l i d da t a b i t va lue s a r e (de f au l t i s 8 ) : 4 , 5 , 6 , 7 o r 8 .

The va l i d s t op b i t va lue s a r e (de f au l t i s 1 ) . 1 , 1 . 5 o r 2 .

An example o f s e t t i ng a con t ro l po r t t o 4800Baud , even pa r i t y , 7 da t a

b i t s and 1 s t op b i t i s : Com1 .Se t t i ngs = "4800 ,E ,7 ,1"

CommPort

The CommPor t p rope r ty s e t s and r e tu rns t he commun ica t i on po r t

numbe r . I t s syn t ax i s :

[ f o rm . ]MSComm. CommPor t = por tNumber[%]

which de f i ne s t he po r tNumber f rom a va lue be tween 1 and 99 . A va lue

o f 68 i s r e t u rned i f t he po r t does no t ex i s t .

Por tOpen

The Po r tOpen p rope r ty s e t s and r e tu rns t he s t a t e o f t he

commun ica t i ons po r t . I t s syn t ax i s :

[ f o rm . ]MSComm. Por tOpen = [ {True | Fa l s e } ]

A True s e t t i ng opens t he po r t , wh i l e a Fa l s e c l o se s t he po r t and

c l ea r s t he r e ce ive and t r ansmi t bu f f e r s ( t h i s au toma t i ca l l y happens

when an app l i c a t i on i s c l o sed ) . The fo l l owing example opens

commun ica t i ons po r t numbe r 1 (COM1: ) a t 4800 Baud w i th even

pa r i t y , 7 da t a b i t s and 1 s t op b i t :

Input t ing da ta

The t h r ee ma in p rope r t i e s u sed t o r e ad da t a f rom the r e ce ive

bu f f e r a r e Inpu t , I nBuf f e r Coun t and InBuf f e rS i ze .

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Input

The Inpu t p rope r ty r e t u rn s and r emoves a s t r i ng o f cha rac t e r s f rom

the r e ce ive bu f f e r . I t s syn t ax i s :

[ f o rm . ]MSComm. Inpu t

To de t e rmine t he number o f cha rac t e r s i n t he bu f f e r t he

InBuf f e rCoun t p rope r ty i s t e s t ed ( t o be cove red i n t he nex t s ec t i on ) .

Se t t i ng Inpu tLen t o 0 c ause s t he Inpu t p rope r ty t o r e ad t he en t i r e

con t en t s o f t he r e ce ive bu f f e r .

InBuf ferS i ze

The InBuf f e rS i ze p rope r ty s e t s and r e tu rns t he max imum number

o f cha rac t e r s t ha t c an be r e ce ived i n t he r e ce ive bu f f e r ( by de fau l t i t

i s 1024 by t e s ) . I t s syn t ax i s :

[ f o rm . ]MSCommInBu f f e rS i z e = [numBy te s%]

The s i z e o f t he bu f f e r shou ld be s e t so t ha t i t c an s t o r e t he max imum

number o f cha rac t e r s t ha t w i l l be r e ce ived be fo re t he app l i c a t i on

p rog ram can r ead t hem f rom the bu f f e r .

The InBuf f e rCoun t p rope r ty r e t u rn s t he number o f cha rac t e r s i n

t he r e ce ive bu f f e r . I t c an a l so be u sed t o c l e a r t he bu f f e r by s e t t i ng

t he number o f cha rac t e r s t o 0 . I t s syn t ax i s :

[ f o rm . ]MSCommInBuf fe rCoun t= [ coun t%]

Output t ing da ta

The t h r ee ma in p rope r t i e s u sed t o wr i t e da t a t o t he t r ansmi t bu f f e r

a r e Ou tpu t , Ou tBuf f e rCoun t and Ou tBuf f e rS i ze .

The Ou tpu t p rope r ty wr i t e s a s t r i ng o f cha rac t e r s t o t he t r ansmi t

bu f f e r . I t s syn t ax i s :

[ fo rm . ]MSComm. ou tpu t= [ou tS t r i ng$ ]

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OutBuf ferS i ze

The Ou tBuf f e rS i ze p rope r ty s e t s and r e tu rns t he number o f

cha rac t e r s i n t he t r ansmi t bu f f e r ( de f au l t s i z e i s 512 cha rac t e r s ) . I t s

syn t ax i s :

[ f o rm . ]MSCommOutBuf f e r s i z e = [NumByte s%]

OutBu f f e rCoun t

The Ou tBuf f e rCoun t p rope r ty r e t u rn s t he number o f cha rac t e r s i n

t he t r ansmi t bu f f e r .The t r ansmi t bu f f e r c an a l so be c l e a r ed by s e t t i ng

i t t o 0 . I t s syn t ax i s :

[ fo rm . ]MSCommOutBuf f e rCoun t . = [0 ]

5 .3 . FLOW CHART

5.3 .1 . Micro Contro l l e r

Algor i thm

STEP 1 : S t a r t t he p rog ram

STEP 2 : Check whe the r r i ng s i gna l i s p r e sen t o r no t .

STEP 3 : I f r i ng s i gna l i s p r e sen t , make t e l ephone OFF HOOK and

s end FF t o Pe r sona l Compu te r , e l s e go t o STEP 2 .

STEP 4 : Ge t t he DTMF s igna l t h rough t he DTMF decode r .

STEP 5 : Check whe the r # i s p r e s sed o r no t . I f # i s p r e s sed , t hen

d i s connec t t he phone and go t o STEP 2 .

STEP 6 : I f # i s no t p r e s sed , t hen s end t he DTMF da t a t o t he pc

t h rough t he s e r i a l po r t and go t o STEP 4 .

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72

5 .3 .2 . VISUAL BASIC

Algor i thm

STEP 1 : S t a r t t he p rog ram

STEP 2 : Check fo r t he da t a FF .

STEP 3 : I f da t a FF i s p r e sen t , p l ay t he we l come message , e l s e go

t o s t ep 2 .

STEP 4 : P l ay t he message t o en t e r t he ro l l numbe r .

STEP 5 : Check whe the r f ou r number s a r e en t e r ed o r no t .

STEP 6 : I f ye s , p l ay message t o en t e r

1 ATTENDENCE

2 MARKS

# DISCONNECT

e l s e go t o s t ep 5 .

STEP 7 : I f numbe r 1 i s p r e s sed , t hen check t he a t t endance and p l ay

p r e sen t o r absen t message and go t o s t ep 6 .

STEP 8 : I f numbe r 1 i s no t p r e s sed , check whe the r number 2 i s

p r e s sed o r no t . I f so p l ay t he ma rks fo r t he co r r e spond ing

r o l l numbe r and go t o s t ep 6 .

STEP 9 : I f numbe r 2 i s no t p r e s sed , check whe the r number # i s

p r e s sed o r no t . I f so t e rmina t e t he p rog ram and go t o s t ep 2 .

STEP 10 : I f numbe r # i s no t p r e s sed , go t o s t ep 6 un t i l # i s p r e s sed .

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74

6 . PCB DESIGN

6.1 COMPONENT LAYOUT

75

6 .2 . PCB Des ign

The PCB des ign s t a r t s r i gh t f r om the s e l ec t i on o f t he

l amina t e s .The two ma in t ypes o f ba se l amina t e a r e epoxy g l a s s and

pheno l i c pape r l amina t e s a r e gene ra l l y u sed fo r s imp le c i r cu i t s .

Though i t i s ve ry cheap and can ea s i l y be d r i l l ed , pheno l i c pape r ha s

poo r e l e c t r i c a l cha rac t e r i s t i c s and i t ab so rbs more mo i s tu r e t han

epoxy g l a s s . Epoxy g l a s s ha s h ighe r mechan i ca l s t r eng th .

The impor t an t p rope r t i e s t ha t have t o be cons ide red fo r

s e l e c t i ng t he PCB subs t r a t e a r e t he d i e l e c t r i c s t r eng th , i n su l a t i on

r e s i s t ance , wa t e r abso rp t i on p rope r ty , coe f f . o f t he rma l

expans ion , shea r s t r eng th , ha rdnes s , d imens iona l s t ab i l i t y e t c .

6 .3 . PCB Fabr i ca t ion

The f ab r i c a t i on o f a PCB inc ludes fou r s t eps .

a ) P repa r ing t he PCB pa t t e rn .

b ) T rans f e r r i ng t he pa t t e rn on to t he PCB.

c ) Deve lop ing t he PCB.

d ) F in i sh ing ( i . e ) d r i l l i ng , cu t t i ng , smoo th ing , t u rn ing e t c .

Pa t t e rn de s ign ing i s t he p r ima ry s t ep i n f ab r i c a t i ng a PCB. In

t h i s s t ep , a l l i n t e r connec t i on be tween t he componen t s i n t he g iven

c i r cu i t a r e conve r t ed i n to PCB t r acks . Seve ra l f a c to r s such a s

pos i t i on ing t he d i ame te r o f ho l e s , t he a r ea t ha t e ach componen t wou ld

occupy , t he t ype o f end t e rmina l shou ld be cons ide red .

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Trans ferr ing the PCB Pat t ern

The coppe r s i de o f t he PCB shou ld be t ho rough ly c l e aned w i th

t he he lp o f a l coho l i c sp i r i t o r pe t ro l . I t mus t be comple t e ly f r e e f rom

dus t and o the r con t aminan t s .

The mi r ro r image o f t he pa t t e rn mus t be c a rbon cop i ed and t o t he

l amina t e t he comple t e pa t t e rn may now be made each r e s i s t an t w i th

t he he lp o f pa in t and t h in b rush .

Deve lop ing

I n t h i s deve lop ing a l l exce s s ive coppe r i s r emoved f rom the boa rd

and on ly t he p r i n t ed pa t t e rn i s l e f t beh ind . Abou t 100ml o f t ap wa t e r

shou ld be hea t ed t o 75 ° C and 30 .5 g r ams o f FeC l 3 added t o i t , t he

m ix tu r e shou ld be t ho rough ly s t i r r ed and a f ew d rops o f HCl may be

added t o speed up t he p roce s s .

The boa rd w i th i t s coppe r s i de f a c ing upward shou ld be p l aced i n

a f l a t bo t t omed p l a s t i c t r ay and t he aqueous so lu t i on o f FeC l 2 pou red

i n t he e t ch ing p roce s s wou ld t ake 40 t o 60 min t o comple t e .

A f t e r e t ch ing t he boa rd i t shou ld be washed unde r runn ing wa t e r

and t hen he ld aga in s t l i gh t . t he p r i n t ed pa t t e rn shou ld be c l e an ly

v i s i b l e . The pa in t shou ld be r emoved w i th t he he lp o f t h inne r .

Fin i sh ing Touches

A f t e r t he e t ch ing i s comple t ed , ho l e o f su i t ab l e d i ame te r shou ld

be d r i l l ed , t hen t he PCB may be t i n p l a t ed u s ing an o rd ina ry 35 Wa t t s

so lde r i ng rod a long w i th t he so lde r co re , t he coppe r s i de may be

g iven a coa t o f va rn i sh t o p r even t ox ida t i on .

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Dri l l ing

Dr i l l s f o r PCB use u sua l l y come wi th e i t he r a s e t o f co l l e c t s o f

va r i ous s i z e s o r a 3 - J aw chuck . Fo r a ccu racy howeve r 3 - j aw chunks

a r en ’ t b r i l l i an t and sma l l d r i l l be low 1 mm f rom g rooves i n t he j aws

p r even t i ng good g r i p s .

So lder ing

Beg in t he cons t ruc t i on by so lde r i ng t he r e s i s t o r s f o l l owed by

t he capac i t o r s and t he LEDs d iodes and IC socke t s . Don’ t t r y

so lde r i ng an IC d i r ec t l y un l e s s you t ru s t you r sk i l l i n so lde r i ng . A l l

componen t s shou ld be so lde red a s shown in t he f i gu re . Now connec t

t he sw i t ch and t hen so lde r / s c r ew i f on t he PCB us ing mu l t i p l e washe r s

o r space s . So lde r i ng i t d i r e c t l y w i l l on ly r educe i t s he igh t above o the r

componen t s and hampe r i n i t s e a sy f i xa t i on i n t he c ab ine t . Now

connec t t he ba t t e ry l e ad .

Assembl ing

The c i r cu i t c an be enc lo sed i n any k ind o f c ab ine t . Be fo re

f i t t i ng t he PCB su i t ab l e ho l e s mus t be d r i l l ed i n t he c ab ine t f o r t he

sw i t ch , LED and buzze r . No t e t ha t a r o t a ry sw i t ch can be u sed i n s t ead

o f a s l i de t ype .

Swi t ch on t he c i r cu i t t o be de s i r ed r ange . I t w i l l au toma t i ca l l y

s t a r t i t s t im ing cyc l e s . To be su r e t ha t i t i s work ing p rope r ly wa t ch

t he LED f l a sh . The componen t s a r e s e l ec t ed t o t r i gge r t he a l a rm a f ew

minu t e s be fo re t he s e t l im i t .

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7 . CONCLUSION

Embedded sys t em p l ays a ma jo r r o l e i n advanced commun ica t i on

sy s t em. Embedded sys t em i s t he cu r r en t t e chno logy and ha s a b r i gh t

f u tu r e . Any r ea l t ime app ly can be con t ro l l ed . Our p ro j ec t w i l l be

ve ry ob l i g ing t o t he pa r en t s t o be acqua in t ed w i th t he i r

son ’ s /daugh t e r ’ s r e c i t a l i n t he co l l ege . P r e sen t a t i on i n t he c l a s s and

ou t come o f t he un ive r s i t y a r e made r eachab l e t o t he pa r en t s by ou r

p ro j ec t . Moreove r , t he t ime spend ing fo r co l l ege o f f i c i a l s i n

a t t emp t ing phone ca l l s f r om ou t s i de r s w i l l be r educed .

We had succe s s fu l l y execu t ed ou r p ro j ec t “VISCA” by u s ing ou r

co l l ege t e l ephone l i ne .

9 . FUTURE ENHANCEMENT

Our p ro j ec t shou ld be mod i f i ed t o know the p ro f i l e o f t he

s t uden t .

Acces s t he co l l ege da t abase fo r t he execu t i on o f ou r p ro j ec t .

Sound shou ld be mod i f i ed by r eco rd ing t he sound i n a sound

p roo f room.

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APPENDIX 1

INSTRUCTION SET OF MCS51 FAMILY

Table: 1 Arithmetic Instruction for MCS51

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Table: 2 Logical Operations

81

Table: 3 Data Transfer Instruction

82

83

Table: 4 Boolean Variable Manipulations and Machine Control

Instructions

REFERENCES

84

1 . Kenne th . J .Aya l a (Second ed i t i on ) . “The 8051 Mic rocon t ro l l e r

A rch i t e c tu r e , p rog ramming and app l i c a t i ons” .

2 . Muhammad Al i Maz id i , J an i ce G i l l i sp i e Maz id i . ( 2002 )

THE 8051 MICROCONTROLLER AND EMBEDDED SYSTEMS

3 . Mohammed Azam, P rog ramming w i th V i sua l Bas i c 6 .0

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