[General] How to interface ADC0804 with 8051?

alvinmuji · May 28, 2014

Hi, any idea how to interface ADC0804 with 8051? I conenct the ADC0804 D7-D0 (Pin Pin 11 – Pin 18) to the 8051 P2.7 - P2.0 (Pin 28 – Pin 21). However, its not giving me the expected result. then I tried on ADC0804 chip itself and it does work with LED indication. but when interface with 8051, it just couldn't work. this is the code I used, can anyone advice? Thanks in advance!

Code:

#include <ds89c4xx.h>

sbit adc_port = P2; //ADC port
sbit rd = P0^2; //Read signal P0.2
sbit wr = P0^1; //Write signal P0.1
sbit cs = P0^3; //Chip Select P0.3 (((pin5 of pull up)))
sbit intr = P0^0; //INTR signal P0.0
sbit mybit = P0^7; //high/low compare value result

void conv(); //Start of conversion function
void read(); //Read ADC function

unsigned char adc_data;

void main() {

while (1) { //Forever loop
conv(); //Start conversion
read(); //Read ADC

if (adc_data <= 0X40) //Send the read and compare if value is less than 40 in hex, 64 in decimal. More than 50cm away <1.25V { mybit=1 ; // set P0.7 high } else { mybit=0 ; // set P0.7 low }
} }

void conv() {
cs = 0; //Make CS low
wr = 0; //Make WR low
wr = 1; //Make WR high (start conversion)
cs = 1; //Make CS high
while (intr); //Wait for INTR to go low
}

void read() {
cs = 0; //Make CS low
rd = 0; //Make RD low
adc_data = adc_port; //Read data from ADC0804 port
rd = 1; //Make RD high
cs = 1; //Make CS high
}

memarian · May 28, 2014

Hi,

Your program has 2 Errors :

1) You can't use this : sbit adc_port = P2; . This is not correct. sbit only defines a bit not a full port(or full byte).
check this : https://www.keil.com/support/man/docs/c51/c51_le_sbit.htm

2) Because P2 is your input port , You should write 0xFF in P2 before you start read operation.if you don't connect P2 to any other peripheral and it's only used as a input port, you need to write 0xff only once,but if you use P2 as Input/output port,you need to write 0xFF before every read operation.

and also i assume that you used Pull-Up resistors on your P0 Port (that you used to send commands to ADC). Correct?

Good Luck!

MANO.5 · May 28, 2014

CS is an active low input to activate ADC0804. so CS must be grounded always...

try this

Code C - [expand]
1
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sbit RD=P2^0;
sbit WR=P2^1;
sbit INTR=P2^2;
sfr MYDATA=P1;

in main function

Code C - [expand]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
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16
MYDATA=0xFF;
RD=1;
WR=1;
 INTR=1;
 
while(1)
{
  WR=0;
 WR=1;
while(INTR==1)
 RD=0;
 value=MYDATA;
  convert(value);
   display(value);   //in lcd
    RD=1;
}

alvinmuji · May 30, 2014

Hello Memarian,

Thanks for your reply and pointing out out error. I did the changes and find that my ADC0804 (D7-D0) is always '1111 1111' as P2 is tied to the adc0804 (D7-D0)... and yup! I used Pull-Up resistors on the P0 Port !

Code:

#include <ds89c4xx.h> 

sbit rd = P0^2; //Read signal P0.2
sbit wr = P0^1; //Write signal P0.1
sbit cs = P0^3; //Chip Select P0.3
sbit intr = P0^0; //INTR signal P0.0
sbit mybit = P0^7; //high/low compare value result

void conv(); //Start of conversion function
void read(); //Read ADC function

unsigned char adc_data;

void main() {

P2 = 0XFF;	 //set P2 as input
while (1) { //Forever loop
conv(); //Start conversion
read(); //Read ADC

if (adc_data <= 0X40)      //Send the read and compare if value is less than 40 in hex, 64 in decimal. More than 50cm away <1.25V
		{
		mybit=1 ;             // set P0.7 high 	
		}
		else
		{
		mybit=0 ;             // set P0.7 low
		}
}
}

void conv() {
cs = 0; //Make CS low
wr = 0; //Make WR low
wr = 1; //Make WR high (start conversion)
cs = 1; //Make CS high
while (intr); //Wait for INTR to go low
}

void read() {
cs = 0; //Make CS low
rd = 0; //Make RD low
adc_data = P2; //Read data from ADC0804 port
rd = 1; //Make RD high
cs = 1; //Make CS high
}

alvinmuji · May 30, 2014

Thanks for your reply and pointing out out error. I did the changes and find that my ADC0804 (D7-D0) is always '1111 1111' as P2 is tied to the adc0804 (D7-D0)... and yup! I used Pull-Up resistors on the P0 Port !

Code:

#include <ds89c4xx.h> 

sbit rd = P0^2; //Read signal P0.2
sbit wr = P0^1; //Write signal P0.1
sbit cs = P0^3; //Chip Select P0.3
sbit intr = P0^0; //INTR signal P0.0
sbit mybit = P0^7; //high/low compare value result

void conv(); //Start of conversion function
void read(); //Read ADC function

unsigned char adc_data;

void main() {

P2 = 0XFF;	 //set P2 as input
while (1) { //Forever loop
conv(); //Start conversion
read(); //Read ADC

if (adc_data <= 0X40)      //Send the read and compare if value is less than 40 in hex, 64 in decimal. More than 50cm away <1.25V
		{
		mybit=1 ;             // set P0.7 high 	
		}
		else
		{
		mybit=0 ;             // set P0.7 low
		}
}
}

void conv() {
cs = 0; //Make CS low
wr = 0; //Make WR low
wr = 1; //Make WR high (start conversion)
cs = 1; //Make CS high
while (intr); //Wait for INTR to go low
}

void read() {
cs = 0; //Make CS low
rd = 0; //Make RD low
adc_data = P2; //Read data from ADC0804 port
rd = 1; //Make RD high
cs = 1; //Make CS high
}

memarian said:
Hi,

Your program has 2 Errors :

1) You can't use this : sbit adc_port = P2; . This is not correct. sbit only defines a bit not a full port(or full byte).
check this : https://www.keil.com/support/man/docs/c51/c51_le_sbit.htm

2) Because P2 is your input port , You should write 0xFF in P2 before you start read operation.if you don't connect P2 to any other peripheral and it's only used as a input port, you need to write 0xff only once,but if you use P2 as Input/output port,you need to write 0xFF before every read operation.

and also i assume that you used Pull-Up resistors on your P0 Port (that you used to send commands to ADC). Correct?

Good Luck!

memarian · May 31, 2014

Hi,
Can you post your schematic (circuit)?

It seems that your program is ok,but for some reason maybe there is some faults somewhere else.

BTW : what is your microcontroller clock? DS89c4xx are not normal 8051! Normal 8051 has machine cycle=Clock/12 , but in DS89c4xx usually machine cycle=1 Clock ! if your microcontroller clock is too high, your timing will have some problems. (For example after enabling Read, you must wait between 125 ... 200 ns for valid data).

phongphanp · May 31, 2014

In many datasheet had testing diagram such as initial command .

More error bits rate, More tolelance not noise.

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[General] How to interface ADC0804 with 8051?

alvinmuji

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memarian

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alvinmuji

MANO.5

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alvinmuji

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alvinmuji

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memarian

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