Detecting NACK response from slave after write?

Sridhar Rajagopal92

Other Parts Discussed in Thread: CC3200

Hi,

I have an i2c slave (Microchip MCP39F521) and one of the commands returns a nack when the command does not succeed.

I expect the I2C_transfer that I do to return false, but it does not.

int autoCalibrateGain()
{
	  uint8_t aucWriteDataBuf[4];
	  int i;
	  I2C_Handle      i2c;
	  I2C_Params      i2cParams;
	  I2C_Transaction i2cTransaction;
	  uint32_t checksumTotal = 0;

	  /* Create I2C for usage */
	  I2C_Params_init(&i2cParams);
	  i2cParams.bitRate = I2C_100kHz;
	  i2c = I2C_open(Board_I2C_TMP, &i2cParams);
	  if (i2c == NULL) {
	      System_printf("[MCP39F521] Error Initializing I2C\n");
	      return 0;
	  }
	  else {
	      System_printf("[MCP39F521] I2C Initialized!\n");
	  }
	   System_printf("[MCP39F521] After I2C init\n");


	   aucWriteDataBuf[0] = 0xa5; // Header
	   aucWriteDataBuf[1] = 0x04; // Num bytes
	   aucWriteDataBuf[2] = 0x5a; // Command
	   aucWriteDataBuf[3] = 0x03; // checksum

	   i2cTransaction.slaveAddress = 0x74;
	   i2cTransaction.writeBuf = aucWriteDataBuf;
	   i2cTransaction.writeCount = 4;
	   i2cTransaction.readBuf = NULL;
	   i2cTransaction.readCount = 0;

	   System_printf("[MCP39F521] Before I2C_transfer\n");

	   if (I2C_transfer(i2c, &i2cTransaction)) {
		    System_printf("[MCP39F521] I2C write complete\n");
	   }
	   else {
	        System_printf("[MCP39F521] I2C write failed 1\n");
	        /* Deinitialized I2C */
	        I2C_close(i2c);
	        System_printf("[MCP39F521] I2C Closed\n");
	        return 0;
	   }

	   /* Deinitialized I2C */
	   I2C_close(i2c);
	   System_printf("[MCP39F521] I2C Closed\n");
	   return 1;


}

In my particular case, I expect the command write to give me a NACK, and so for the I2C_transfer to return false.

TABLE 4-9: AUTO-CALIBRATE GAIN COMMAND
Byte # Value Byte Description Response from MCP39F521
1 0xA5 Header Byte
2 0x04 Number of Bytes in Frame
3 0x5A Command (Auto-Calibrate Gain)
4 0x03 Checksum ACK (or NAK if unable to calibrate), 
see Section 8.0,MCP39F521 Calibration for more information.

I'm wondering if my understanding of I2C_transfer is right in this circumstance?

Thanks,

Sridhar

over 9 years ago

0 Vikram Adiga over 9 years ago

TI__Genius 10825 points

Hi Sridhar,

Which version of TI-RTOS are you using? Can you also tell us the device that you are using?

The I2C_transfer should return false when a NACK is received. From the I2C driver docs, the return value will be:

In I2C_MODE_BLOCKING: true on successful transfer; false on an error, such as an I2C bus fault (NACK). In I2C_MODE_CALLBACK: always true. The transferCallbackFxn's bool argument will be true if successful; false on an error, such as an I2C bus fault (NACK).

Can you make sure that the i2C slave is sending the master a NACK (with a scope)?

Thanks,

Vikram

0 Sridhar Rajagopal92 over 9 years ago in reply to Vikram Adiga

Intellectual 560 points

Hi Vikram,

Thanks for your response. I'm using TI-RTOS 2.16.01.14 with CC3200, and using the blocking mode.

I figured out the problem. The MCP39F521 sends back an ack or a nack as a 1 byte header that needs to be read. I was not doing the reading of the 1 byte response. Once I did that everything worked as expected.

Thanks,
Sridhar

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Detecting NACK response from slave after write?