How to read the temperature of DS1620 thermometer using PIC16F877A?

Question

Good afternoon.

I am trying to figure out how to make a PIC16F877A to read the temperature from the DS1620 sensor. Accordingly to the datasheet of the DS1620, I need to send two nibbles A (AAh) to the sensor and may it return the bytes with the temperature. This is what I've tried until now.

However, since in the datasheet isnt specified the protocol (only says 3-wire communication), I am trying some bit-banging, with no success.

This is the code of what I've tried until now:

#define DQ RC0_bit
#define CLK RC1_bit
#define RST RC2_bit

unsigned int resp;
int rcv;

void clock() {
      CLK = ~CLK;
      Delay_ms(10);
}

int readSensor() {
     int cont = 0;
     RST = 0x00;
     CLK = 0;
     Delay_ms(30);
     resp = 0;

     while (cont <= 16) {
       clock();
       resp |= DQ;
       resp = resp<<1;
       clock();
       cont++;
     }
 
     RST = 0x01;
     Delay_ms(30);
     return resp;
}

void writeSensor(char ch) {
     int cont = 0;
     RST = 0x00;
     CLK = 0;
     Delay_ms(30);
     resp = 0;

     while (cont <= 16) {
       DQ = ch & 0b00000001;
       clock();
       ch = ch>>1;
       clock();
       cont++;
     }

     RST = 0x01;
     Delay_ms(30);
     RST = 0x00;
     Delay_ms(30);
     RST = 0x01;
     Delay_ms(30);
}

void main() {

    UART1_Init(9600);               // Initialize UART module at 9600 bps

    UART1_Write_Text("Start");  UART1_Write(10);  UART1_Write(13);

    TRISC = 0b00000000;
    PORTC = 0b00000100;
 
    writeSensor(0xAA);
    Delay_ms(30);
    rcv = readSensor();
 
    Delay_ms(100);                  // Wait for UART module to stabilize

    UART1_Write(rcv);
 
}

Here are the circuit in Proteus:

I am new in bit banging and PIC, but I have some experience with C language.

May you say (or do some approach) what am I missing in order to read the temperature of this thermometer?

Answer 1

I'm not totally familiar with the PIC, but after looking at the code for a DS1820 Arduino library:

https://github.com/msparks/arduino-ds1620/blob/master/DS1620.cpp

I would make sure you are changing the DQ pin to an input when reading and an output when writing.

The other thing I noticed is that the Arduino library follows this procedure for reading each bit:

1. Bring the clock line LOW
2. Read the DQ pin
3. Bring the clock line HIGH

And your code does:

1. Begin with CLK = 0
2. Toggle CLK
3. Read DQ
4. Toggle CLK
5. Goto 2

So you are reading DQ when CLK is high.

There's probably no need for such a large delay in your clock() routine.