The 8051 Microcontroller and Embedded

Department of Computer Science and Information EngineeringNational Cheng Kung University

17

‰INTERFACING TO ADC AND SENSORSADC804 Chip (cont’) HANEL

Analog ground and digital ground¾Analog ground is connected to the ground of the analog V

in

¾Digital ground is connected to the ground of the V

ccpin

‰To isolate the analog V

signal from in

transient voltages

caused by digital

switching of the output D0 – D7¾This contributes to the accuracy of the digital data output

+5V^20 VCC 618 D0Vin(+) 717 D1Vin(-)^168 D2A GND^159 D3/2V^14 refD4 1913 CLK RD5^12 D6^11 D7 4 CLK in^3 WR^5 INTR 1 CS 2 RD 10 D GND

Department of Computer Science and Information EngineeringNational Cheng Kung University

18

‰ INTERFACING TO ADC AND SENSORSADC804 Chip (cont’) HANEL
The following steps must be followed for data conversion by the ADC804 chip¾Make CS = 0 and send a low-to-high pulse to pin WR to start conversion¾Keep monitoring the INTR pinƒIf INTR is low, the

conversion is finished

ƒIf the INTR is high, keep polling until it goes low¾After the INTR has become low, we make CS = 0 and send a high-to-low pulse to the RD pin to get the data out of the ADC804 D0-D7

Data out

Start conversion

End conversion

Read it

CS WR INTRRDCS is set to low for both RD and WR pulses

Department of Computer Science and Information EngineeringNational Cheng Kung University

19

ADC804 Free Running Test ModeINTERFACING TO ADC AND SENSORSTesting ADC804 HANEL

+5V^206789194351210

10kPOT 10k150 pF

To LEDs normallyopenSTART

Vin(+)D0D1Vin(-)D2A GNDD3/2VrefD4CLK RD5D6D7CLK inCSRDD GND

The binary outputs are monitored on the LED of the digital trainerVCC (^1817161514131211) WRINTR The CS input is grounded and the WR input is connected to the INTR output
a potentiometer used to apply a 0-to-5 V analog voltage to input Vin (+) of the 804 ADC
Department of Computer Science and Information EngineeringNational Cheng Kung University
20
Examine the ADC804 connection to the 8051 in Figure 12-7. Write a program to INTERFACING TO ADC AND SENSORSTesting ADC804(cont’) HANEL
monitor the INTR pin and bring an analog input into register A. Then call a hex-to ACSII conversion and data display subroutines. Do this continuously.;p2.6=WR (start conversion needs to L-to-H pulse);p2.7 When low, end-of-conversion);p2.5=RD (a H-to-L will read the data from ADC chip);p1.0 – P1.7= D0 - D7 of the ADC804;MOV P1,#0FFH
;make P1 = input
BACK: CLR P2.6
;WR = 0
SETB P2.6
;WR = 1 L-to-H to start conversion
HERE: JB P2.7,HERE
;wait for end of conversion
CLR P2.5
;conversion finished, enable RD
MOV A,P1
;read the data
ACALL CONVERSION
;hex-to-ASCII conversion
ACALL DATA_DISPLAY
;display the data
SETB p2.5
;make RD=1 for next round
SJMP BACK