PIC16F84 Code for the NK0E Weather Station Project

; PIC16F84 code for the NK0E weather station project. The purpose; of this project is to provide a hardware interface which measures; temperature, wind speed, wind direction, humidity, and pressure; and communicates it to a PC via serial communications when; requested. Note that the data collected and transmitted must be; processed by the PC in order to obtain the actual measurement; values (i.e. no calibration is done in the PIC code).;; The hardware circuit makes use of two major components: the ; PIC16F84 itself and a MAX232 TTL-RS232 level converter.; The MAX232 converts the TTL signals from the PIC to RS232 levels; for the PC (and vice versa).;; The PIC16F84 pin assignments are as follows:;; RA1: serial out to PC; RA2: clock out to SHT11 temp/humid sensor; RA3: data in/out for SHT11 temp/humid sensor; RB0: serial in from PC (generates interrupt);; This software implements the following command set:;; Received Reply Description;-----------------------------------; 't' 12345 CR LF Get the temperature raw data. Five digits; or e1 CR LF are always returned, with leading zeroes; or e2 CR LF if necessary, followed by a carriage return; and line feed. See the SHT11 data sheet; for instructions on computing the temperature.; A return of e1 indicates that the SHT11 didn't; acknowledge the request. A return of e2; indicates that no data was returned by the SHT11; within the wait period (255 ms).; 'h' 12345 CR LF Get the humidity raw data. Five digits; or e1 CR LF are always returned, with leading zeroes; or e2 CR LF if necessary, followed by a carriage return; and line feed. See the SHT11 data sheet for; instructions on computing the humidity.; A return of e1 indicates that the SHT11 didn't; acknowledge the request. A return of e2; indicates that no data was returned by the SHT11

; within the wait period (255 ms).; 'v' version info Gets the version number of the firmware.; returns an ASCII string followed by a ; carriage return and line feed.;; Written using Microchip MPLAB v5.40;; Please direct any questions, comments, or suggestions to the; author: David Ek; [email protected];; History:;; Rev 1 (23 Jul 2002):; Creation. Returns dummy temperature data. This version used; for installment 2 of the PIC WX articles in QQ.; Rev 2 (26 Sep 2002):; Added code for the Sensirion SHT11 temperature/humidity sensor; for installment 3 of the PIC WX articles in QQ.;;----------------------------------------------------------------

list p=16f84radix dec__config _CP_OFF & _WDT_OFF & _XT_OSC

include "p16f84.inc"

; defines:

; These are used by the serial comm routines for timing. Note that; slower speeds may not work well because the delays might be larger; than 255, requiring the use of the prescalar.

_Clkspd equ 1000000 ;external clock / 4_BaudRate equ 9600 ;desired baud rate_Period equ (_Clkspd/_BaudRate) ;clock cycles / bit

_StartRxDelay equ (_Period/2 - 15)/3 ;this is how long to;wait to get to the;middle of the start;bit. This is loops,;not clock cycles.

_BitRxDelay equ 277 - _Period ;this is what to load;into TMR0 for correct;interval between bits;on RX

_BitTxDelay equ 285 - _Period ;this is what to load;into TMR0 for correct;interval between bits;on TX

_StopTxDelay equ 272 - _Period ;this is what to load;into TMR0 for correct;interval betweeen last;bit and stop bit on TX

; defines for I/0 pins:

_SER_IN equ 0 ;Serial input line (PORTB)_SER_OUT equ 1 ;Serial output line (PORTA)_SHT11_SCK equ 2 ;clock line for SHT11 sensor

;(PORTA)_SHT11_DAT equ 3 ;data line for SHT11 sensor

;(PORTA)

; macros for the bin-to-ascii conversion routines:

loadw macro arg1movlw high(arg1)movwf himovlw low(arg1)movwf loendm

dodigit macro arg1movlw high(arg1)movwf shimovlw low(arg1)movwf slocall dosubendm

; memory locations:

cblock 0x0C

BitCount ;number of bits left to send or;receive, not including start & stop;bits

RXChar ;received character while being receivedRXBuff ;most recently received character

TXChar ;character to transmit

SerialReg ;status register:;bit 0: on if character has been; received;bit 1: on if busy with RX/TX

;bit 2: on if sending, off if receiving;bit 3: on if next bit to send is stop bit

WSave ;copy of W register

SSave ;copy of the Status register

SHT11Byte ;a byte of data sent to or returned by the SHT11

counter ;generic counter register

hi ;hi byte for number to be converted to asciilo ;lo byte for number to be converted to asciishi ;hi byte for subtractor for conversion to asciislo ;lo byte for subtractor for conversion to asciidigit ;ascii digit converted from binary. Also used as

;input to SendErrorCode

MSDelay ;register for WaitMS timing

endc

org 0x00goto Main

org 0x04

;--------------------------------------------------------------------;-----Serial Communication Routines----------------------------------;--------------------------------------------------------------------;; The serial comm routines generate 1 start bit, 8 data bits, 1 stop bit, ; no parity. The baud rate is determined by the delay programmed; into the onboard timer. The sending and receiving is interrupt driven,; meaning other tasks can be carried on while the characters are being; sent and received.;;-----Main Interrupt Routine-----------------------------------------;; for timing: 4 cycles from interrupt time to get here.

; Save the W and STATUS registers:

Intmovwf WSave

swapf STATUS,W ;use swapf to prevent anymovwf SSave ;status flags from being changed

; cycles so far since interrupt occurred: 7

; Okay, I'm doing something goofy here. Instead of actually checking; the overflow bits themselves, I'm using the enable bits to determine; which interrupt occurred. I can do this because there should only; ever be one type of interrupt active at a time. The problem with; checking the overflow bits is that the T0IF bit can get set even; if that interrupt is disabled.

; Check first for a timer overflow interrupt. The overflow bit gets; set even if the interrupt is disabled.

btfsc INTCON,T0IEgoto DoBit ;we're in the middle of sending or

;receiving

; 10 cycles executed on entry to DoBit

; If not a timer overflow interrupt, check for external interrupt:

btfsc INTCON,INTE ;RB0 is our receive line and itgoto StartRX ;generates an interrupt on a high-

;to-low transition

; 12 cycles executed on entry to StartRX

; Else, must be something we don't care about:

;do nothing for now

; Restore the W and STATUS registers:

Restore swapf SSave,Wmovwf STATUSswapf WSave,Fswapf WSave,W

retfie

;------end Main Interrupt Routine------------------------------------

;------Subroutine SerSetup-------------------------------------------

SerSetup

; set up the option register for internal counting, WDT disabled,; no prescaler.

clrf TMR0bsf STATUS,RP0clrwdt ;set bits in OPTION_REG tomovlw b'10001000' ;enable internal clock counting,movwf OPTION_REG ;disable watchdog timer.bcf STATUS,RP0 ;switch to bank 0

; set the output line to idle (high)

bsf PORTA,_SER_OUT ;set the output line to idle;(high) state

movlw b'00000001'movwf PORTB

; enable the external interrupt via RB0

movlw b'10010000' ;set bits in INTCON to enablemovwf INTCON ;external interrupt

; initialize the SerialReg:

clrf SerialReg

return

;------end SetSetup--------------------------------------------------

;------Subroutine StartRX--------------------------------------------;; This subroutine is called by the main interrupt routine when an; external interrupt on RB0 occurs. This means we're receiving the; start bit for a character. We want to enable the external TMR0; interrupt and prepare to receive the character.

StartRX

; wait halfway through the bit to see if it's real:

bcf INTCON,INTF ;clear the interrupt

movlw _StartRxDelaymovwf BitCount ;this is the 15th instruction since

;the interrupt. Note--we're using;BitCount for this loop purely for;convenience. Usually it's used to;actually count the bits we TX/RX.

RXWait decfsz BitCount,F ;this loop takes 3 times the initial

goto RXWait ;value of BitCount clock cycles

; now we should be at the middle of the start bit. Is the input still; low? If not, goto Restore and ignore this interrupt.

btfsc PORTB,_SER_INgoto Restore

; if we get to here it must really be the start bit. Load TMR0,; disable the external interrupt, and enable the TMR0 interrupt.

; load up the appropriate delay to get us to the middle of the; first bit:

movlw _BitRxDelaymovwf TMR0 ;4 cycles from read of PORTBmovlw b'00100000'movwf INTCON

; set the SerialReg to indicate that the routines are busy getting; a character:

movlw b'00000010'movwf SerialReg

; initialize BitCount:

movlw 8movwf BitCount

; okay, now we return.

goto Restore

;------end StartRX---------------------------------------------------

;------DoBit---------------------------------------------------------;

; sends or receives the next bit. Bits are sent/received from least; to most significant bit.

DoBit

; clear the TMR0 overflow interrupt flag:

bcf INTCON,T0IF

; Are we receiving?

btfsc SerialReg,2goto Sending

; check to see if we're receiving the stop bit:

movf BitCount,Fbtfsc STATUS,Zgoto GetStopBit

; if we get to here, we're in the middle of receiving. Get the next; bit: (16 cycles to get to the next instruction from the start of; the interrupt).

rrf PORTB,W ;rrf PORTB into W. This sets;the carry bit if RB0 was high.

rrf RXChar,F ;doing a rrf on RXChar brings;in the carry bit to the MSB.

; Decrement the bit counter.

decf BitCount,F

; reload TMR0 for the next interrupt, and; go to the end of the interrupt routine.

movlw _BitRxDelaymovwf TMR0 ;21 cycles from start of interruptgoto Restore

; if we get to here it's because we need to check for the stop bit.

GetStopBitbtfss PORTB,_SER_IN ;is the RX line low? If so, it's notgoto Done ;the stop bit. Otherwise, set themovlw b'00000001' ;SerialReg to show a character hasmovwf SerialReg ;been receivedmovf RXChar,W ;copy the received character to RXBuff

movwf RXBuffgoto Done

; We got here because we're sending.; check to see if we're finished sending the stop bit:

Sendingbtfsc SerialReg,3goto Done

; check to see if we need to send the stop bit:

movf BitCount,Fbtfsc STATUS,Z ;18th cyclegoto SendStopBit

; if we get to here, we're in the middle of sending. Send the next; bit: (16 cycles to get to the next instruction from the start of; the interrupt).

rrf TXChar,F ;doing rrf on TXChar puts thebtfss STATUS,C ;least significant bit in thegoto SendZero ;carry flag.nopbsf PORTA,_SER_OUT ;if carry is set, send a one.goto EndDoBit ;PORTA,1 is set on the 24th cycle

SendZerobcf PORTA,_SER_OUT ;otherwise, send a zero. (24th cycle)nop ;nop's are for taking the same timenop ;to get to reloading TMR0 as for when

;a one is sent.

; Decrement the bit counter.

EndDoBitdecf BitCount,F


movlw _BitTxDelaymovwf TMR0 ;29th cyclegoto Restore

; Here we need to send the stop bit, turn off the TMR0 interrupt,; turn on the external interrupt, and set the SerStatus register; flags appropriately.

SendStopBitnopnopnopbsf PORTA,_SER_OUT ;no. Send the stop bit. (24th cycle)bsf SerialReg,3 ;set the "sending stop bit" flag


movlw _StopTxDelaymovwf TMR0 ;27th cyclegoto Restore

; we're completely done sending or receiving. Clean up.

Done movlw b'00010000' ;set bits in INTCON to enablemovwf INTCON ;external interruptmovlw b'00000001'andwf SerialReg,F ;clear the busy bits in SerialReggoto Restore

;------end DoBit-----------------------------------------------------

;------Subroutine SendChar-------------------------------------------;; This is not called by the interrupt handler. Rather, it activates ; the interrupts needed to send it. Put the character to be sent in; the TXChar file register before calling this subroutine.;

SendChar

; send the start bit:

bcf PORTA,_SER_OUT

; set the SerStatus to indicate that the routines are busy sending; a character:

movlw b'00000110'movwf SerialReg

; load up TMR0 so it overflows at the right time.

nop ;for timingmovlw _BitTxDelay

movwf TMR0 ;5th cycle after write to PORTA

; clear the external interrupt flag, disable the external interrupt,; and enable the TMR0 interrupt.

movlw b'10100000'movwf INTCON

; set the BitCount for the eight bits to send:

movlw 8movwf BitCount

return

;------end SendChar--------------------------------------------------

;------begin GetAChar------------------------------------------------

GetACharcall Idlebtfss SerialReg,0 ;wait for a character to be receivedgoto GetACharbcf SerialReg,0return

;------end GetAChar--------------------------------------------------

;------begin SendAChar-----------------------------------------------

SendACharcall SendChar

WaitToFinishcall Idlebtfsc SerialReg,1 ;wait for the character to be sentgoto WaitToFinishreturn

;------end SendAChar-------------------------------------------------

;------Subroutine WaitMS---------------------------------------------;; WaitMS is an approximate millisecond delay. It assumes a 4 MHz

; oscillator, meaning instructions are executed at a rate of 1 MHz.; I got the timing info (number of cycles per instruction) from the; Microchip PIC16F84 data sheet.

; the call to this subroutine takes 2 cycles to execute.

WaitMSmovlw 248 ;1 cyclemovwf MSDelay ;1 cyclenop ;1 cycle--these nops are added to nop ;1 cycle make the total number ofnop ;1 cycle instructions executed in

; the routine to be 1000.;the nop instruction simply does ;nothing except take time to execute.

; The loop below takes four cycles for every time through except the; last, when it takes five (including the time needed to execute the; return). So, the total number of instructions executed in getting; to and returning from this subroutine is:;; 2 to get here; + 2 to set the MSDelay value; + 3 for the nops; + 247*4 for the first 247 times through the loop; + 5 for the last time through the loop and to return; --------; = 1000

RepeatWaitMSnop ;1 cycledecfsz MSDelay,F ;1 cycle if not zero, 2 if zerogoto RepeatWaitMS ;2 cyclesreturn ;2 cycles

;------end WaitMS----------------------------------------------------

;------begin SHT11TXRX-----------------------------------------------;; Sends a byte command to the SHT11 temp/humidity sensor and retrieves; a two-byte response. Sends the response back to the PC as an ASCII; string representation of the number.;

; Put the byte to send in SHT11Byte before calling this routine.

SHT11TXRX

;make _SHT11_DAT an output

bsf STATUS,RP0 ;switch to bank 1bcf TRISA,_SHT11_DAT ;make Port A data line an outputbcf STATUS,RP0 ;switch back to bank 0

;send the Transmission Start sequence:

bsf PORTA,_SHT11_DAT ;set the data line highbsf PORTA,_SHT11_SCK ;take the clock line highbcf PORTA,_SHT11_DAT ;take the data line lowbcf PORTA,_SHT11_SCK ;take the clock line lowbsf PORTA,_SHT11_SCK ;take the clock line high againbsf PORTA,_SHT11_DAT ;set the data line high again

;load up the counter to loop through the eight bits to send:

movlw 8movwf counter

SHT11SendBitLoopbcf PORTA,_SHT11_SCK ;take the clock line low

btfss SHT11Byte,7 ;is the next bit to send a one?goto SHT11SendZero ;nope. Go send a zero.bsf PORTA,_SHT11_DAT ;if it's a one, send it.goto SHT11SendBit

SHT11SendZerobcf PORTA,_SHT11_DAT ;set the data line to zero

SHT11SendBitbsf PORTA,_SHT11_SCK ;take the clock line high to send

rlf SHT11Byte,F ;move the next bit into MSB

decfsz counter,F ;dec the counter and check for zero.goto SHT11SendBitLoop ;if not zero, more bits to send

bcf PORTA,_SHT11_SCK ;take the clock line low

;no more bits to send. Set the data line to be an input and;wait for the ack from the SHT11:

bsf STATUS,RP0 ;switch to bank 1bsf TRISA,_SHT11_DAT ;make Port A data line an inputbcf STATUS,RP0 ;switch back to bank 0

; now look for an ack (SHT11 pulls data line low--should; happen on the next rise of the SCK line). If it doesn't; happen, return an 'e' and quit.

bsf PORTA,_SHT11_SCK

SHT11WaitAckbtfss PORTA,_SHT11_DATgoto SHT11GotAck

;if we don't get an ack, quit, send an 'e1' for error and return.

movlw '1'movwf digitcall SendErrorCodegoto SHT11TXRXDone

; we got an Ack. Get ready for the data to be returned. take; the clock line low, and then wait for the data line to be; pulled low again.

SHT11GotAckbcf PORTA,_SHT11_SCK

; now wait for the data. It takes approximately 210 ms for; the temperature measurement, or 55 ms for the humidity; measurement, so we'll wait up to 255 ms before giving up.


SHT11WaitDatabtfss PORTA,_SHT11_DATgoto SHT11DataReadycall WaitMSdecfsz counter,Fgoto SHT11WaitData

;if we don't get the data, quit, send an 'e2' error and return.

movlw '2'movwf digitcall SendErrorCodegoto SHT11TXRXDone

SHT11DataReady

; get the most sig byte:

call SHT11GetByte

movf SHT11Byte,Wmovwf hicall SendAck ;acknowledge the byte

; get the least sig byte:

call SHT11GetBytemovf SHT11Byte,Wmovwf locall SendAck ;acknowledge the byte

call SHT11GetByte ; gets the checksum (not needed)

; Send the data as ASCII:call SendAsciiNum

; Send the terminating CR and LF:call SendCRLF

SHT11TXRXDonereturn

;------end SHT11TXRX--------------------------------------------------

;------begin SHT11GetByte---------------------------------------------;; Gets a byte of data from the SHT11. Assumes that the data; is ready to be sent by the SHT11. Also assumes that _SHT11_DAT has; been set to input. Also assumes that _SHT11_SCK has been set to low.; Returns the byte in SHT11Byte.

SHT11GetByte; clear SHT11Byte:

clrf SHT11Byte

; set counter to get eight bits


SHT11GetByteLoopbsf PORTA,_SHT11_SCK ;set the clock high to get the next

bitbtfss PORTA,_SHT11_DAT ;is the next bit a one?goto SHT11GetZeroBit ;no--it's a zerobsf SHT11Byte,0 ;if it's a one, set the LSB in

SHT11Byte

goto SHT11GotBit

SHT11GetZeroBitbcf SHT11Byte,0 ;set the LSB to zero in SHT11Byte

SHT11GotBitbcf PORTA,_SHT11_SCK ;set the clock line low again.decfsz counter,Fgoto SHT11GetNextBitgoto SHT11GetByteDone

SHT11GetNextBitrlf SHT11Byte,F ;move the bits over to get the next

bitgoto SHT11GetByteLoop

SHT11GetByteDone

return

;------end SHT11GetByte-----------------------------------------------

;------begin SendAck-------------------------------------------------;; send the ack. Set the data line as an output:

SendAckbsf STATUS,RP0 ;switch to bank 1bcf TRISA,_SHT11_DAT ;make Port A data line an outputbcf STATUS,RP0 ;switch back to bank 0

; now send the ack. Take the data line low.

bcf PORTA,_SHT11_DATbsf PORTA,_SHT11_SCKbcf PORTA,_SHT11_SCK

; now make the data line an input again.

bsf STATUS,RP0 ;switch to bank 1bsf TRISA,_SHT11_DAT ;make Port A data line an inputbcf STATUS,RP0 ;switch back to bank 0

return

;------end SendAck---------------------------------------------------

;------begin SendErrorCode-------------------------------------------

;; send error code back to PC. Error code is 'e' plus a digit. Load; ASCII value of digit into 'digit' register before calling.

SendErrorCodemovlw 'e'movwf TXCharcall SendACharmovf digit,Wmovwf TXCharcall SendACharcall SendCRLFreturn

;------end SendErrorCode---------------------------------------------

;------begin TellTemperature-----------------------------------------

;This subroutine is called when the 't' command is received. Calls;SHT11TXRX.

TellTemperature

movlw 3movwf SHT11Bytecall SHT11TXRX

goto MainLoop

;------end TellTemperature-------------------------------------------

;------begin TellHumidity--------------------------------------------

;This subroutine is called when the 'h' command is received. Calls;SHT11TXRX.

TellHumidity

movlw 5movwf SHT11Bytecall SHT11TXRX

goto MainLoop

;------end TellHumidity----------------------------------------------

;------begin SendCRLF------------------------------------------------;; Send the terminating CR and LF:

SendCRLFmovlw 13movwf TXCharcall SendACharmovlw 10movwf TXCharcall SendACharreturn

;------end SendCRLF--------------------------------------------------

;------begin SendAsciiNum--------------------------------------------;; load lo, hi with 16 bit unsigned num to send

SendAsciiNumdodigit 10000movf digit,Wmovwf TXCharcall SendAChardodigit 1000movf digit,Wmovwf TXCharcall SendAChardodigit 100movf digit,Wmovwf TXCharcall SendAChardodigit 10movf digit,Wmovwf TXCharcall SendACharmovf lo,w ; ls byte is already correctaddlw '0' ; convert to asciimovwf TXCharcall SendACharreturn ; done

; "dosub" is called by the "dodigit" macro defined above.; Subtract the number in shi/slo from hi/lo until the result; is negative, incrementing the ascii equivelent each time.

dosub movlw '0'-1movwf digit

moresub incf digit,F ; increment ASCII charactermovf slo,w ; subtract current power of 10subwf lo,fmovf shi,wbtfss STATUS,Caddlw 1subwf hi,fbtfsc STATUS,C ; any carry?goto moresub ; no, keep subtracting

movf slo,w ; reverse the last subtractionaddwf lo,fmovf shi,wbtfsc STATUS,Caddlw 1addwf hi,freturn

;------end SendAsciiNum----------------------------------------------

;------begin ReportVersion-------------------------------------------

; send a string with the version in it. The string comes from EEPROM; memory and is null-terminated. The null terminator is not sent. The; protocol dictates that the string sent is terminated by a CR, which; is sent. This subroutine is called when the 'v' command is received.

ReportVersionbcf STATUS,RP0clrf EEADR ;the string we want starts at the

;beginning of EEPROM memory.

GetNextVersionCharbsf STATUS,RP0bsf EECON1,RDbcf STATUS,RP0movf EEDATA,Wbtfsc STATUS,Z ;if the character in W is null, don't

;send any more.goto MainLoop

movwf TXCharcall SendACharincf EEADR,F

goto GetNextVersionChar

;------end ReportVersion---------------------------------------------

;------begin Idle----------------------------------------------------;; Idle should be called whenever the chip is waiting for something; to happen (waiting for a character to be sent or received, for; example). Here it's not doing anything.

Idlereturn

;------end Idle------------------------------------------------------

;------Main Program--------------------------------------------------

Main

; set up the ports as inputs and outputs as needed.

bsf STATUS,RP0 ;switch to bank 1movlw 0xFFmovwf TRISB ;make Port B inputmovlw 0x00movwf TRISA ;make Port A outputbcf STATUS,RP0

clrf PORTA

call SerSetup ;set up serial comm routines & int.

; this main program simply waits for characters to be received, then; calls the handler for the command indicated by the received character.

MainLoopcall GetAChar ;wait for a character

movf RXBuff,W ;move the rx char into Wsublw 't' ;compare with 't' characterbtfsc STATUS,Zgoto TellTemperature ;if t, report the temperature

movf RXBuff,W ;move the rx char into Wsublw 'h' ;compare with 'h' character

btfsc STATUS,Zgoto TellHumidity ;if h, report the humidity

movf RXBuff,W ;move the rx char into Wsublw 'v' ;compare with 'v' characterbtfsc STATUS,Zgoto ReportVersion ;if v, report the version number

goto MainLoop

;------Version EEPROM------------------------------------------------

org 0x2100de "WxPIC v0.3b (c) 2002 by NK0E",0x0D,0x0A,0x00 ;

Version 0.3bend

PIC16F84 Code for the NK0E Weather Station Project

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