TWI starting

[rago]

Hello guys I tried to start TWI bus and got a lot of questions. (NRF51 1422 AC)

I added necessary libraries, could You tell me what more i need to include in my code :

    #define TWI_MASTER_CONFIG_CLOCK_PIN_NUMBER (0U)
#define TWI_MASTER_CONFIG_DATA_PIN_NUMBER (2U)
//
static const nrf_drv_twi_t m_twi = NRF_DRV_TWI_INSTANCE(0);
static nrf_drv_twi_config_t nrf_drv_twi_config =
{	.scl = TWI_MASTER_CONFIG_CLOCK_PIN_NUMBER,
	.sda = TWI_MASTER_CONFIG_DATA_PIN_NUMBER,
	.frequency = NRF_TWI_FREQ_100K,
	.interrupt_priority = 0};

 void nrf_drv_twi_initialize(void){
	 
 nrf_drv_twi_init(&m_twi, &nrf_drv_twi_config, 0, NULL);
	nrf_drv_twi_enable(&m_twi);
	 
 }
 
 void nrf_drv_twi_uninitialize(void){
	 
	nrf_drv_twi_uninit(&m_twi);
	nrf_drv_twi_disable(&m_twi);
	 
 } 

and

nrf_drv_twi_tx(&m_twi,(0x49<<1),&read_adress,1,true);

nrf_drv_twi_rx(&m_twi,(0x49<<1),&value1, 1);

But is not working for me. Could u answer me too, operation (0x49<<1) with sensor adress is necessary with our example ?

[MartinBL]

Hi

The left shifting of the address is always a source of confusion (and of good reasons). The thing is that the TWI operates with 7-bit addresses, but whenever you perform a TX or RX the address is left shifted once. This is usually done for you by hardware (or the driver). Then the Least Significant Bit (LSB) is set to either '0' or '1' to indicate whether you want to do a RX or a TX operation respectively.

So in binary, address 0x49 equals: 1001001b

• During a RX operation the address + LSB exposed on the TWI lines will be 10010010b
• During a TX operation the address + LSB exposed on the TWI lines will be 10010011b

Since the LSB of 0x49 is a '1' I think it is safe to assume that the address you use is a 7-bit address.

Now to the confusing part; The datasheets of TWI devices haven't really decided on how to define the device address. Some manufacturers define the address as a 7-bit value meant to be left shifted before setting LSB to '0' or '1'. Others define the address as an 8-bit value where you are not meant to do any left shifting, but only set the LSB to '0' or '1'. In addition to this, TWI drivers might not always clarify whether it wants a 7 or 8-bit address, with or without the read/write bit already set.

I looks like you use SDK 11(?) though, so the transfer functions want a 7-bit address, e.g. 0x49.

From the brief of nrf_drv_twi_tx():

 * @param[in] address    Address of a specific slave device **(only 7 LSB).**

Other than that your code looks fine, but it seems like you have initiated your TWI driver in blocking mode, as you have not passed a TWI event handler to nrf_drv_twi_init(). This means that your code will stay in nrf_drv_twi_xx() forever if something goes wrong (e.g. if you use the wrong address).

Finally I would suggest that you try to debug your code like this. It might give you a clue of what the TWI driver is up to.