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Connecting Altimeter to nrf52 dk using i2c.

Hi I trying to connect Altimeter ( mpl 3115a2) to the nrf52 development kit. Can someone guide me how to do it (pin connection). I have followed the example given in the sdk but still I am a little unclear. Thank you.

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  • In the twi_master_with_twis_slave example the pins and twi/s instances are defined in the file config.h:

    #define TWI_SCL_M                3   //!< Master SCL pin
    #define TWI_SDA_M                4   //!< Master SDA pin
    
    #define MASTER_TWI_INST          0    //!< TWI interface used as a master accessing EEPROM memory
    

    The macros are used in twi_master_init():

        const nrf_drv_twi_config_t config =
        {
           .scl                = TWI_SCL_M,
           .sda                = TWI_SDA_M,
    ...
    

    So in the example you can change TWI_SCL_M and TWI_SDA_M to be 27 and 26 respectively to match your circuit.

    The simulated EEPROM (slave) address is also defined in config.h:

    #define EEPROM_SIM_ADDR          0x50 //!< Simulated EEPROM TWI address
    

    and the address is used like so:

        static ret_code_t eeprom_read(size_t addr, uint8_t * pdata, size_t size)
        {
    ...
               ret = nrf_drv_twi_tx(&m_twi_master, EEPROM_SIM_ADDR, &addr8, 1, true);
    ...
               ret = nrf_drv_twi_rx(&m_twi_master, EEPROM_SIM_ADDR, pdata, size, false);
    ...
        }
    

    So EEPROM_SIM_ADDR above would in your altimeter's case be changed to 0xC0 (datasheet p.6. ; 7bit address 0x60 << 1). Otherwise the reads and writes are done similarly to how they're done in the example.

    As for the read/write (register) addresses, you need to follow e.g. the sequence in MPL3115A2 datasheet p.10. IIC_RegWrite/Read are analogous to eeprom_write/read in the example (size=1).

    I hope I managed to answer your question and didn't just blabber something... :)

  • Your read_reg() returns the unitialized ret, not the actual register value. Poll the STATUS register until it is 1 and then do the reading. Currently you read the register once and it's too early for the data to be ready.

    So you should have something like

    // reads a single 8-bit register and returns its value
    static uint8_t read_reg( uint8_t slave_address, uint8_t register_address) {
        uint8_t buff;
        nrf_drv_twi_tx(&m_twi_master, slave_address, &register_address, 1, true);
        nrf_drv_twi_rx(&m_twi_master, slave_address, &buff, 1, false);
        return buff;
    }
    

    and

    // initialization, activation
    
    // read the status register until PTDR is set
    while( !(read_reg(0x60, 0x00) & 0x08) );
    
    // data should be ready when we get out of the while loop
    // read_reg() and print
    
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  • Your read_reg() returns the unitialized ret, not the actual register value. Poll the STATUS register until it is 1 and then do the reading. Currently you read the register once and it's too early for the data to be ready.

    So you should have something like

    // reads a single 8-bit register and returns its value
    static uint8_t read_reg( uint8_t slave_address, uint8_t register_address) {
        uint8_t buff;
        nrf_drv_twi_tx(&m_twi_master, slave_address, &register_address, 1, true);
        nrf_drv_twi_rx(&m_twi_master, slave_address, &buff, 1, false);
        return buff;
    }
    

    and

    // initialization, activation
    
    // read the status register until PTDR is set
    while( !(read_reg(0x60, 0x00) & 0x08) );
    
    // data should be ready when we get out of the while loop
    // read_reg() and print
    
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