CCS Exercise on I2C

[Guest_X44]

I’m following the example set out in the CCS Exercise book. P. 17, on using the I2C Temperature Sensor (device is DS1631).

There are a few things I still don’t quite understand. Perhaps, someone here can shed some light.

According to the datasheet, initiating a 2-wire communication requires for the Master (in this case the PIC16F877) to generate a START followed by a CONTROL BYTE – in this case, i2c_write(0x90), then followed by a COMMAND BYTE, which indicates what type of operation is to be performed.

But, looking at the definition inside the init_temp(), in the call to i2c_write(0xee), the parameter 0xee is not among the command protocols in the COMMAND SET listed in the datasheet.

Question: What then is this for if it’s not a command protocol in the COMMAND SET?

Question: What is the temp_config(BYTE data) for, although it makes sense that the temp_config(BYTE data) is called because I recognise that the 12c_write(0xac) corresponds to one of the command protocols in the COMMAND SET. If the temp_config(BYTE data is to configure the device then why is this not called first?



#include <16f877.h>
#device ICD=TRUE
#fuses HS, NOLVP, NOWDT, PUT
#use delay(clock=20000000)
#use rs232(DEBUGGER)

#ifndef DAL_SCL
#define DAL_SCL PIN_B0
#define DAL_SDA PIN_B1
#endif

#define read_temp read_high_temp // for backwards compatability

#use i2c(master,sda=DAL_SDA, scl=DAL_SCL)


void temp_config(BYTE data) {

i2c_start();
i2c_write(0x90);
i2c_write(0xac);
i2c_write(data);
i2c_stop();
}


void init_temp() {
output_high(DAL_SDA);
output_high(DAL_SCL);
i2c_start();
i2c_write(0x90);
i2c_write(0xee);
i2c_stop();
temp_config(8);
}


BYTE read_high_temp() { // Returns degrees F (0-255)
BYTE datah,datal;
signed long data;

i2c_start();
i2c_write(0x90);
i2c_write(0xaa);
i2c_start();
i2c_write(0x91);
datah=i2c_read();
datal=i2c_read(0);
i2c_stop();

data=datah;
data=data*9;
if(bit_test(datal,7))
{
if(data < 0)
data -= 4;
else
data += 4;
}
data=(data/5)+32;

if(data < 0)
data = 0;
else if(data > 255)
data = 255;

return((int)data);
}


signed int read_low_temp() { // Returns degrees F (-67 to 127)
signed int datah, datal;
signed long data;

i2c_start();
i2c_write(0x90);
i2c_write(0xaa);
i2c_start();
i2c_write(0x91);
datah=i2c_read();
datal=i2c_read(0);
i2c_stop();

data=datah;
data=data*9;
if(bit_test(datal,7))
{
if(data < 0)
data -= 4;
else
data += 4;
}
data = (data / 5) + 32;

if(data > 127)
data = 127;

return((int)data);
}


signed long read_full_temp() { // Returns degrees F (-67 to 257)
signed int datah, datal;
signed long data;

i2c_start();
i2c_write(0x90);
i2c_write(0xaa);
i2c_start();
i2c_write(0x91);
datah=i2c_read();
datal=i2c_read(0);
i2c_stop();

data=datah;
data=data*9;
if(bit_test(datal,7))
{
if(data < 0)
data -= 4;
else
data += 4;
}
data = (data / 5) + 32;

return(data);
}




main()
{
byte value;
init_temp();

do{
value = read_temp();
printf("%u\r\n", value);
delay_ms(1000);
}while(TRUE);
}

[PCM programmer]

The code that you posted, with the 0xEE command, is from ds1621.c,
not ds1631.c. That file is available in the following folder:
c:\Program Files\Picc\Drivers
So there's either a problem in the exercise book, or you misread it.

[Guest]

The circuit in the exercise book shows a ds1621.

Thank you so much, PCM Programmer.