Problems Sequential reading channels ADC MCP3424 via I2C

AlexanderH

Hello, I am Alexander and probing a lot with Rexygen, with good results until now. However, at this moment I am trying to read data with the Rexlang block (I2C communication) from an ADC (analog-digital converter) MCP3424, without succes. I am relatively new with respect to the Rexlang block and i2c. I know that I have to send a not-acknowledge (NAK) bit and a stop bit to exit the current read operation and send a new read command for the latest conversion data. However I don't know how to do that.

Hopefully somebody is willing to help me with my problem.
Many thanks in advance.

Below my code:

/************************************************************
*
* REXLANG - Reading data from MCP3424 AD converter via I2C
*
*************************************************************/

string parameter(0) i2c_dev; // the I2C bus is defined by the p0 parameter

//assigning variables to outputs, these variables are WRITE-ONLY
long output(0) channel1; // output of value of ADC channel 1
long output(1) channel2; // output of value of ADC channel 2
long output(2) channel3; // output of value of ADC channel 3
long output(3) channel4; // output of value of ADC channel 4

//declaration of variables
long i2c_bufTx[3]; //buffer for transmitting data
long i2c_bufRx[3]; //buffer for receiving data
long i2c_bus_handle;
long i2c_chip_address;
long i2c_write_count;
long i2c_read_count;
long i2c_ret_fun;

//the init procedure is executed once when the REXLANG function block initializes
int init(void)
{
  i2c_bus_handle = OpenI2C(i2c_dev); // open I2C bus
  /* Address: 1 1 0 1 A2 A1 A0 */
  i2c_chip_address = 0x68; // 7-bit address of the I2C device
  
  return 0;
}

//the main procedure is executed once in each sampling period
long main(void)
{
  /* Configuration register: 
     =====================================================================================
     | bit 7                | bit 6-5        | bit 4          | bit 3-2     | bit 1-0      |
     -------------------------------------------------------------------------------------
     | 1 = start conversion | 00 = channel 1 | 1 = continuous | 00 = 12-bit | 00 = gain x1 |
     | 0 = no effect        | 01 = channel 2 | 0 = one-shot   | 01 = 14-bit | 01 = gain x2 |
     |                      | 10 = channel 3 |                | 10 = 16-bit | 10 = gain x4 |
     |                      | 11 = channel 4 |                | 11 = 18-bit | 11 = gain 8x |
     =====================================================================================
  */
  i2c_bufTx[0] = 0x90; // read channel 1, continuous, 12bit, gain 1 (see MCP3424 datasheet)
  i2c_write_count = 1;
  i2c_read_count = 2;
  //Sending data via I2C
  i2c_ret_fun = I2C(i2c_bus_handle, i2c_chip_address, i2c_bufTx, i2c_write_count, i2c_bufRx, i2c_read_count);
  channel1 = ((i2c_bufRx[0]<<8) + i2c_bufRx[1])/2;
  
  return  0;

  i2c_bufTx[0] = 0xB0; // read channel 2 continuous, 12bit, gain 1 (see MCP3424 datasheet)
  i2c_write_count = 1;
  i2c_read_count = 2;
  //Sending data via I2C
  i2c_ret_fun = I2C(i2c_bus_handle, i2c_chip_address, i2c_bufTx, i2c_write_count, i2c_bufRx, i2c_read_count);
  channel2 = ((i2c_bufRx[0]<<8) + i2c_bufRx[1])/2;
  
  return 0;
}

//the exit procedure is executed once when the task is correctly terminated
// (system shutdown, downloading new control algorithm, etc.)
long exit(void)
{
  if(i2c_bus_handle>=0) Close(i2c_bus_handle); // close I2C bus
  return 0;
}