TMS320F28335: F28335

Hi Anu,

Anu B said:

But why can't we initially set the NACK bit and then poll the NACK bit (I2CSTR.1)? Thus, if it becomes 0, then it means acknowledgement has been sent by the receiver.

Writing a 1 to the I2CSTR.NACK bit will manually clear it to 0, so this will not work. The NACK bit is intended for detecting NACKs, not ACKs.

Anu B said:

SCD/ARDY can indicate only if the number of bytes set in I2CCNT has been transmitted. Without polling NACK how can we know if the slave has received the data?

You can utilize an interrupt to handle NACKs when they're received. Or use something like the below if polling. Note this is for non-FIFO mode.

    // Transmit Register Bytes
    for (i=0; i< reg_size; i++)
    {
        while(!I2caRegs.I2CSTR.bit.XRDY){} // Make sure data
                                           // is ready to be written
        I2caRegs.I2CDXR = reg[i];
        
        // Add delay here for TX to complete....

        #if NACK_CHECK // check if NACK was received
            if(I2caRegs.I2CSTR.bit.NACK == 1)
            {
                I2caRegs.I2CMDR.bit.STP = 1;
                I2caRegs.I2CSTR.all = I2C_CLR_NACK_BIT;

                Status = I2C_ERROR;
                return Status;
            }
        #endif
    }

Best,

Kevin

Thanks!

But, why do the example codes just poll ARDY and never check if the receiver had actually acknowledged it?

This is what is done:

I2caRegs.I2CCNT = 1; // 1 byte message
I2caRegs.I2CDXR = POINTER_TEMPERATURE;
I2caRegs.I2CMDR.all = 0x6620; // master-receiver, START, STOP
while(I2caRegs.I2CSTR.bit.ARDY == 0); // poll ARDY-  wait for STOP condition

After this, the next transmission starts.

 So, without checking for ACK bit, the next transmission is started. Why is that?  

 Everywhere, its been told that if the slave device does not acknowledge the transfer, then the next data/ transfer can not be initiated. But the example code doesn't do that. So, isn't that supposed to be wrong since we will never know if the receiver had actually received it?