Transmiting only slave address on TWI I2C

[mojangeex]

Hello 
I am using a I2C sensor module and I need to tranmit only address to receive data back, but I dont know how.

 

    err_code = nrf_drv_twi_tx(&m_twi, MICS_VZ_89TE_ADDR,mics_data, sizeof(mics_data),true);
     APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_twi_tx(&m_twi, 0xE1,NULL,0,true);
      APP_ERROR_CHECK(err_code);

     err_code = nrf_drv_twi_rx(&m_twi, MICS_VZ_89TE_ADDR,mics_data, 7);
     APP_ERROR_CHECK(err_code);

Program crashes on line 4.

Thank you for your help.

[bjorn-spockeli]

HI mojoangeex, 

I do not think you can send only the address as message going out on the bus will need to contain the following:

• Start condition
• Stop condition
• Read and write bits
• ACK/NACK bits  
• Address of the Slave
• Data frame

Which SDK version are you using and which nRF device is it running on? Does nrf_drv_twi_tx( return an error code? If so, which? It could be that you have to point to an empty buffer rather than passing a NULL pointer. 

err_code = nrf_drv_twi_tx(&m_twi, 0xE1,NULL,0,true);
APP_ERROR_CHECK(err_code);

Best regards

Bjørn

[mojangeex]

Hello
I am running SDK 15.3 and nRF52832 DK.

Code compiles sucessfully, but the program crashes at executing that line.

err_code = nrf_drv_twi_tx(&m_twi, 0xE1,NULL,0,true);
APP_ERROR_CHECK(err_code);

<00> error> app: Fatal error

00> warning> app: System reset

I need to send message without data frame.

On arduino there is an example:

 Wire.beginTransmission((uint8_t)_i2caddr);
    Wire.write((uint8_t)reg); //This send the command to get data
    Wire.write(0x0);
    Wire.write(0x0);
    Wire.write(0x0);
    Wire.write(0x0);
    Wire.write(0x0);
    Wire.endTransmission();
    
    Wire.beginTransmission(0xE1);
    Wire.endTransmission();

[bjorn-spockeli]

Fatal Error means that the nrf_drv_twi_tx has returned a non-zero error code and this is being caught by the APP_ERROR_CHECK call. Which return code is nrf_drv_twi_tx  returning? You should be able to see this when debugging the application. My guess it that its NRF_ERROR_INVALID_PARAM, i.e. 0x07. If that is the case then try passing an empty buffer instead of a NULL pointer. 

[mojangeex]

Sorry for late response. 

Thank you for response. 

     uint8_t dra[0] ={};
     err_code = nrf_drv_twi_tx(&m_twi, 0xE1,dra,1,false);
      APP_ERROR_CHECK(err_code);

Application does not crash with above code, but I2C device still does not work. I will investigate further and report when I solve it.
Best regards.