MCP7940 drivers for nrf52840

[Vishal Aditya]

We are working on external RTC MCP7940(i2c) interfaced with nrf52840. Please check if drivers of the same for nrf52/51 are available or any implementation of CLOCK using MCP7940 with NRF?

Regards

Vishal Aditya

Embedded Software Engineer

[bjorn-spockeli]

The trace clearly show that its only the MCP7940_I2C address that is transmitted. The nrf_drv_twi_tx documentation states that the data passed to it should be a uint8_t pointer, so try passing it like this

uint8_t tx_data = REG_RTCHOUR;

err_code = nrf_drv_twi_tx(&m_twi,MCP7940_I2C,&tx_data , sizeof(tx_data));

APP_ERROR_CHECK(err_code)

Furthermore what does the bitClear (registerValue, 6) and bitSet (registerValue, 6) functions do? You are passing they're return value as the length parameter to nrf_drv_twi_tx and nrf_drv_twi_rx.

void init_MCP7940() {

    char registerValue = 0x00; // Holds the received register value
    char twelveHour = 0x00; // 0 = 24 Hour Clock Mode / 1 = 12 Hour Clock Mode
    char startClock = 0x01; // 0 = Start Oscillator / 1 = Stop Oscillator
    
    // Turn on/off: 12 hour vs. 24 hour clock
    err_code = nrf_drv_twi_tx(&m_twi,MCP7940_I2C, REG_RTCHOUR, 1);
    err_code = nrf_drv_twi_rx(&m_twi, MCP7940_I2C, registerValue, sizeof(MCP7940_I2C));
    
    if (twelveHour == 0x00) err_code = nrf_drv_twi_tx(&m_twi,MCP7940_I2C, REG_RTCHOUR, bitClear (registerValue, 6));
    if (twelveHour == 0x01) err_code = nrf_drv_twi_tx(&m_twi,MCP7940_I2C, REG_RTCHOUR, bitSet (registerValue, 6));
    
    // Turn on/off: Oscillator (starts the clock)
    err_code = nrf_drv_twi_rx(&m_twi, MCP7940_I2C, registerValue, 1);
    
    if (startClock == 0x00) err_code = nrf_drv_twi_tx(&m_twi,MCP7940_I2C, REG_RTCSEC, bitClear (registerValue, 7));
    if (startClock == 0x01) err_code = nrf_drv_twi_tx(&m_twi,MCP7940_I2C, REG_RTCSEC, bitSet (registerValue, 7));

}

[Vishal Aditya]

Custom defined which works as below:

https://www.arduino.cc/reference/en/language/functions/bits-and-bytes/bitclear/

https://www.arduino.cc/reference/en/language/functions/bits-and-bytes/bitset/

Will update the traces & API call as per this soon!

bjorn-spockeli said:

uint8_t tx_data = REG_RTCHOUR;

err_code = nrf_drv_twi_tx(&m_twi,MCP7940_I2C,&tx_data , sizeof(tx_data));

APP_ERROR_CHECK(err_code)

[Vishal Aditya]

Pls check the trace of REG_RTCHOUR, 

const uint8_t MCP7940_RTCHOUR = 0x02; ///< Timekeeping, RTCHOUR Register address

[bjorn-spockeli]

Yes, now you are writing to register with address 0x02 of the device with address 0xDE, but you are not providing the value you want to write to register 0x02. 

uint8_t tx_data[] = {REG_RTCHOUR, <value to write to REG_RTCHOUR register> };

err_code = nrf_drv_twi_tx(&m_twi,MCP7940_I2C,tx_data , sizeof(tx_data));

APP_ERROR_CHECK(err_code)

[Vishal Aditya]

Pls check

const uint8_t  MCP7940_ST                =         7; ///< MCP7940 register bits. RTCSEC reg
//REST variables remains same as above
	while(1)
	{
	uint8_t tx_data[] = {REG_RTCSEC, MCP7940_ST };
	uint8_t rx_data[] = REG_RTCSEC;

	//trying to start oscillator
		err_code = nrf_drv_twi_tx(&m_twi,MCP7940_I2C,tx_data , sizeof(tx_data),false);
		APP_ERROR_CHECK(err_code);
	  err_code = nrf_drv_twi_rx(&m_twi,MCP7940_I2C,rx_data,1);
		nrf_delay_ms(1);
    }