How do I write a value V to a register R using device address A with nrf_drv_twi ?

[Robert]

I am using nrf51822, sdk version 11.0, sofdevice 130, i2c initialized in non-blocking mode. The read seems ok. The write is problematic for me.

[Jørgen Holmefjord]

Which I2C device are you trying to write to? You will have to look in the datasheet of the device you are interfacing to know how to perform a write operation.

Typically you put the register address and your data into a buffer and then transfers this to the device using a single nrf_drv_twi_tx() call. See for instance the function eeprom_write() in TWIS Slave and TWI Master mode drivers Example in the SDK.

[Robert]

MPU56050. I try to write to register 0x1F value 0xFF.

[Josh Grob]

I think Jorgen points to the best answer. For completeness below are some helper functions I have used to do write/read operations for the nrf twi interface.

//write byte to register
void write_byte(const nrf_drv_twi_t *twi_handle, uint8_t address, uint8_t sub_address, uint8_t *data, bool stop)
        {   
            ret_code_t err_code;
            uint8_t data_write[2];
            
            data_write[0] = sub_address;
            data_write[1] = *data;
                
            err_code = nrf_drv_twi_tx(twi_handle, address, data_write, sizeof(data_write), stop);  
            APP_ERROR_CHECK(err_code);
        }

//reading byte or bytes from register            
void write_forread_byte(const nrf_drv_twi_t *twi_handle, uint8_t address, uint8_t sub_address)
        {   
            ret_code_t err_code;
            
            err_code = nrf_drv_twi_tx(twi_handle, address, &sub_address, sizeof(sub_address), true);  
            APP_ERROR_CHECK(err_code);
        }
    
    char read_byte(const nrf_drv_twi_t *twi_handle, uint8_t address, uint8_t sub_address)
        {   
            ret_code_t err_code;
            uint8_t data; // `data` will store the register data     
            
            write_forread_byte(twi_handle, address, sub_address);
            
            err_code = nrf_drv_twi_rx(twi_handle, address, &data, sizeof(data));
            APP_ERROR_CHECK(err_code);
         
            return data; 
        }
        
    void read_bytes(const nrf_drv_twi_t *twi_handle, uint8_t address, uint8_t sub_address, uint8_t * dest, uint8_t dest_count)
        {   
            ret_code_t err_code;  
            
            write_forread_byte(twi_handle, address, sub_address);
            
            err_code = nrf_drv_twi_rx(twi_handle, address, dest, dest_count);
            APP_ERROR_CHECK(err_code);
        }

[Robert]

I have done this:

uint8_t buffer[] = {0x1FU, 0xFFU};
    nrf_drv_twi_tx(&twi_instance, slave_address, buffer, sizeof(buffer), false);

[Robert]

Hello Josh ! The read is ok, but the still doesn't work. Here is my complete code :

#include "app_util_platform.h" // APP_PRIORITY_HIGH
#include "i2c_interface.h"
#include "nrf_drv_twi.h"

#define SCL_PIN 8
#define SDA_PIN 10

static const nrf_drv_twi_t twi_instance = NRF_DRV_TWI_INSTANCE(0);


void init_i2c(){
    nrf_drv_twi_config_t const config = {
        .scl = SCL_PIN,
        .sda = SDA_PIN,
        .frequency = NRF_TWI_FREQ_100K,
        .interrupt_priority = APP_IRQ_PRIORITY_HIGH
    };
    nrf_drv_twi_init(&twi_instance, &config, NULL, NULL);
    nrf_drv_twi_enable(&twi_instance);
}


//write byte to register
void write_byte(const nrf_drv_twi_t *twi_handle, uint8_t address, uint8_t sub_address, uint8_t *data, bool stop){   
        ret_code_t err_code;
        uint8_t data_write[2];
        data_write[0] = sub_address;
        data_write[1] = *data;
        err_code = nrf_drv_twi_tx(twi_handle, address, data_write, sizeof(data_write), stop);  
        APP_ERROR_CHECK(err_code);
}

//reading byte or bytes from register            
void write_forread_byte(const nrf_drv_twi_t *twi_handle, uint8_t address, uint8_t sub_address){   
        ret_code_t err_code;
        err_code = nrf_drv_twi_tx(twi_handle, address, &sub_address, sizeof(sub_address), true);  
        APP_ERROR_CHECK(err_code);
}

char read_byte(const nrf_drv_twi_t *twi_handle, uint8_t address, uint8_t sub_address){   
        ret_code_t err_code;
        uint8_t data; // `data` will store the register data     
        write_forread_byte(twi_handle, address, sub_address);
        err_code = nrf_drv_twi_rx(twi_handle, address, &data, sizeof(data));
        APP_ERROR_CHECK(err_code);
        return data; 
}

void read_bytes(const nrf_drv_twi_t *twi_handle, uint8_t address, uint8_t sub_address, uint8_t * dest, uint8_t dest_count){   
        ret_code_t err_code;  
        write_forread_byte(twi_handle, address, sub_address);
        err_code = nrf_drv_twi_rx(twi_handle, address, dest, dest_count);
        APP_ERROR_CHECK(err_code);
}

void i2c_write_byte(uint8_t address, uint8_t sub_address, uint8_t *data){
    write_byte(&twi_instance, address, sub_address, data, false);
}


void i2c_read_byte(uint8_t address, uint8_t subaddress, uint8_t * data){
    *data = read_byte(&twi_instance, address-1, subaddress);
}