using a pic to communicate with the DS1803 via I2C

Hi,

I don't know which compiler you use but if ACK is needed after each write command then you miss one between those lines below,

result =WriteI2C(0b10101111); // command: write to both potentiometers
result =WriteI2C(myVolume);

And, this is a Send_Byte function but you use a Read command in it which makes no sense to me. And you use RETURN parameter with this Read command which causes STOPI2C command never runs.

iIf you were using Mikroelektonika C compiler my code would be like below

unsigned char I2C_DS1803_SendByte(signed char myVolume)//char myByte)
{

      I2c_Start(); //sends start bits
      I2c_Wr( 0b01010000 );// 0101 + address
      I2c_Wr(0b10101111); // command: write to both potentiometers
      I2c_Wr(myVolume);

      I2c_Stop();

}

Firat

Hi Firat,

The reason I used a read in there was so I could then return the value now reflected on the potentiometer to PORTD in the main program (Connected to LEDs), so I wouldnt have to be measuring the resistance on the DS1803E-010DS1803E-010 all the time.

I did wonder if the program would ever reach I2C_stop(), but I couldn't stop it before reading the value, now that you have confirmed my first thoughts I will remove it, thanks.(Edit: yes I know I could have: read->store value->Stop_I2C->return value, but i rushed this code).

Its quite difficult obtaining documentation, I havent found anything showing what the I2C_Start does for instance, just says it initialises start conditions (just the start bit?), then I read in the DS1803E-010DS1803E-010 datasheet that upon being addressed the DS1803 acqknowledges once the Master sends a SCK, but I dont know if the I2C_Write() is integrating that already into the code behind the scenes. This is possibly a bottleneck of C compilers, with regards to speedy development, knowing exactly what is used within the functions. I think the only way I am going to resolve this is by dissasembling the thing.

John.

Hi John,

If you use a Read command before a Write command finishes then you cause to fail the Write command process. So, don't use it. John, if a code is written by concerning the protocol specifications, then you don't worry about if there is something missed in the ready-functions. I downloaded the DS1308 datasheet but i could not se any Read command. So the device only accepts WRITE command. So the code sample i have given you should simply work. You can read the pot value with a multimeter to check whether it writes the correct value to the digital pot or not.

Firat

Hi FIRAT:

From the DS1803E-010DS1803E-010 datasheet:

________________________________________________

Reading the DS1803E-010DS1803E-010
As shown in Figure 4, the DS1803E-010DS1803E-010 provides one read command operation. This operation allows the user
to read both potentiometers. Specifically, the R/W bit of the control byte is set equal to a 1 for a read
operation. Communication to read the DS1803E-010DS1803E-010 begins with a START condition which is issued by the
master device. The control byte from the master device will follow the START condition. Once the
control byte has been received by the DS1803E-010DS1803E-010, the part will respond with an ACKNOWLEDGE. The
R/W bit of the control byte as stated should be set equal to ‘1’ for reading the DS1803E-010DS1803E-010.
When the master has received the ACKNOWLEDGE from the DS1803E-010DS1803E-010, the master can then begin to
receive potentiometer wiper data. The value of the potentiometer-0 wiper position will be the first
returned from the DS1803E-010DS1803E-010. Once the eight bits of the potentiometer-0 wiper position has been transmitted,
the master will need to issue an ACKNOWLEDGE, unless it is the only byte to be read, in which case the
master issues a NOT ACKNOWLEDGE. If desired the master may stop the communication transfer at
this point by issuing the STOP condition. However, if the value of the potentiometer-1 wiper position
value is needed, communication transfer can continue by clocking the remaining eight bits of the
potentiometer-1 value, followed by an NOT ACKNOWLEDGE. Final communication transfer is
terminated by issuing the STOP command.

__________________________________________________________

Maybe you have the wrong datasheet.

Iñigo.

Oh, yes. My mistake, you right Iñigo. Thanks for the information. I had kept my eyes on the Table 1 of 2-Wire commands. but documentation speaks itself.

Thanks, again

Firat

Thanks all that replied, I have tried it with Acks and without and still cannot get it working, I am going to build the full circuit this time and use a new DS1803E-010DS1803E-010, I fear the reason for it failing could be due to static.