System Design: Peripheral ICs and ADC04 one channel ADC with voltage reference = 1/2 of maximum permitted analog input • ADC0808 eight channels ADC with voltage reference + and -inputs

System Design: Peripheral

ICs and Interfacing

Chapter 7

2011 Microcontrollers-... 2nd Ed. Raj Kamal

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Lesson 5

ADC - Analog to Digital Converter


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Analog to Digital Conversion (ADC)

� Need of Analog signal to be converted into bits in many applications

� Need a reference input (Vref+) = The maximum input when after conversion output bits= all 1s)

� Need Vref− = The minimum input when after conversion output bits= all 0s)

� Generates Digital output bits proportional to the ADC analog input


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ADC output after conversion of analog

signal

� n-bit ADC (output) = binary number for

Analog input ∗ {(2n)- 1}

(Vref+ − Vref−)


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8-bit ADC example

� Assume that 8-bit ADC Vref+ = 1.275 V and Vref− = 0 V.

� Output bits = all 0s = 00000000 (=0d) when input = 0V,

� Output bits = 10000000 (= 128d) when input = 0.64V and

� Output bits = 11111111 (= 255d) when input = 1.275V


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Example of ADC in a Microcontroller

• 80535 ADC with programmable voltage reference

• 80552 10-bit ADC with 8-ch AMUX (Analog multiplexer- same ADC with multiple analog input channels


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ADC Chips for interfacing

processors buses and MCUs ports

• ADC04 one channel ADC with voltage

reference = 1/2 of maximum permitted analog

input

• ADC0808 eight channels ADC with voltage

reference + and -inputs

• ADC0816 sixteen channels

Example of ADC in a Microcontroller


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Considerations when using an ADC

• Number of bits

• Reference Input single or dual

• Reference programmable or non programmable

• Multi or single channel

• Conversion accuracy

• Sampling rate

• Data throughput rate

• CMOS or Bipolar based


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Condition when using an ADC

• Separate analog ground

• Location nearest possible to a signal

transducer


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• 8 bit ADC

• Interfaces with microcontroller ports or processor data and control bus signals

D0-D7, RD and WR and INTR

• Requires Vref/2 input

• Converted output = 1000 000b output when analog input = Vref/2

• WR input results in start of conversion (SOC)

ADC0804


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• SOC input— very short duration pulse (ns) using a NOT-NAND combination

• RD input results in converted bits at output at D0-D7 bus

• EOC output for end of conversion to tofacilitate Interrupt (INTR) driven IO to the processor

ADC0804


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• Separate analog and digital grounds to

isolate digital transitions noise by direct

connection of ANALOG-GND to supply

GND

• Clock frequency adjustable by external RC

pair timing constant

ADC0804


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VCCEOC

CS

Vin−

S/H

Digital GND

RD

B0-B7

IOWR

Vref/2

A-GND

CLKIN

CLKR

Vin+

INTR

P3.7

SOC

Dec

od

er o

r p

ort

bit

To

R-C pair

P3.6 or

IORD

IC

AN+ input

Vin+

out-

enable

ADC One Channel Vin+ in ADC0804

ADC 0804


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• 8 bit ADC

• Interfaces micro-controller ports or

processor D0-D7, RD, WR, ALE (built in

latch) for channel select through AD2-

AD1-AD0 inputs

• Start of conversion (SOC) using WR

ADC0808


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• SOC input very short duration (ns) pulse using a NOT-NAND combination

• output enable for converted bits on D0-D7 using RD

• EOC output for end of conversion to facilitate interrupt (INTR) driven IO

ADC0808


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separate digital transitions noise by direct

connection of A-GND to supply GND

• Clock frequency input

ADC0808


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VCCEOC

CS

Vin−

Digital GND

RD

B0-B7

IOWR

Vref+

A-GND

CLKIN

CLKR

Vin+ ch0-7

INTR

P3.7

SOC

Dec

od

er o

r p

ort

bit

To

R-C pair

P3.6 or

IORD

IC

out enable

8 Channels ADC

ADC 0804

Vref−


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B0-B7 connects to data AD0-AD7

out-enable

IORD

CS

RDS/H

Ch0 AN+ input

ch0 Vin+

Interfacing ADC0808


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• 8 bit ADC

• Interfaces micro-controller ports or processor data buses (D0-D7), RD, WR, ALE for channel select through AD3-AD2-AD1-AD0 bus inputs (also separate A3-A0),

• WR input for start of conversion (SOC)

ADC0816


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• Separate output enable input for expanding the number of channels

• Analog multiplexer in-built gives the analog output for the filter and S/H inputs and then hold outputs to get analog inputs for conversion (External S/H and filter not needed for channels)

ADC0816


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• SOC input can be very short pulse (ns) using a NOT-NAND combination

• RD input for converted bits on D0-D7

• EOC output for end of conversion to facilitate interrupt (INTR) driven IOs

ADC0816


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separate digital transitions noise by direct

connection of A-GND to supply GND

• Clock frequency input

ADC0816


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ADC 0808

VCCEOC

AMUX output

Vref-Digital GND

RD

B0-B7

IOWR

Vref+

A-GND

CLKIN

CLKR

Vin+Ch0-15

INTR

Vout

RC pair

P3.6 or

IORDIC

ALE IN

out enable

ADC 16- Channels

ChA0-ChA3

P3.7

expansion

control


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B0-B7 connects to data D0-D7

ChA0-ChA3 connects to A0-A3/AD0-AD3

CSout enable

ALE IN

IOWR IORD

CS

RD S/H

AMUX output

VoutVref−

WR


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Table 7.20 - Each Pin signals

Table 7.19 - Functions of

subunits in circuit


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Table 7.21 - Sixteen Addresses in

Exemplary circuit for ADC 08016, when interfacing using An-A7 = 0, A6 =1 A5 = 0 A4 = 0

A3-A2-A2-A1 Channel select bits

CSAn-A4Decoder or port bit


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ADC 0804

VCCEOC

CS

Vin-

S/H

Digital GND

RD

B0-B7IOWR

Vref/2

A-GND

CLKIN

CLKR

Vin+

P2.7 P 2.2 or 3.2

P2.1

C =150 pF

and R = 10k

P2.6

IC

AN+ input

Vin+

ADC0804with 8051

RC


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2.Select ADC write P2.1 = 0

3. Pulse Start ADC write P2.7 = 1, then P2.7 = 0

5. Reset P2.6 and Read P1

4.Wait till INT0 interrupt or till P2.2

1.Initial condition P2.6 = 1,P2.7 = 1, P3.2 = 1


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Interface with 68HC11

68HC11

VCCIRQ

Vref+

GND

R/W

AD0-AD7

Vref-

PE0 Vin+

PE1 Vin+

PE2 Vin+

PE3 Vin+


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Summary


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• ADC Bits at output

• ADC 0804,0808, 0816

• Internal AMUX and channel address latch

• Multi channel ADC

• ADC Interfacing to ports

We learnt

System Design: Peripheral ICs and ADC04 one channel ADC with voltage reference = 1/2 of maximum permitted analog input • ADC0808 eight channels ADC with voltage reference + and -inputs

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