NRF52840 I2C ADDRESS.

[sne_333]

Hello Everyone,

                           I am working on NRF52840 development kit. I am trying to run I2c master. My main goal is to send some data to slave via I2C lines. I am using the example code "TWI scanner" from the sdk examples. I have attached the slave microcontroller (ATSAMD20) and I am running i2c slave code on it. The Slave address is 0x54. I have set it as 0x54 in the slave code. Now when I try to scan the devices from NRF52840, the device is found at 0x28 address. Why is it so?? 

[sne_333]

Thanks for your reply Kenneth. Something weird is happening at my side. I agree with your left bit shifting. I tried to test the code again. Now NRF52840 is scanning 2 addresses. 

my code is as follows:-

int main(void){

ret_code_t err_code;
uint8_t address = (0x54U); 
uint8_t data;
bool detected_device = false;
bool result = false;

APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
NRF_LOG_DEFAULT_BACKENDS_INIT();

NRF_LOG_INFO("TWI scanner started.");
NRF_LOG_FLUSH();
twi_init();
nrf_delay_ms(1000); // give some delay

for (address = 1; address <= TWI_ADDRESSES; address++)
{
err_code = nrf_drv_twi_rx(&m_twi, address, &data, sizeof(data));
if (err_code == NRF_SUCCESS)
{
detected_device = true;
NRF_LOG_INFO("TWI device detected at address 0x%x...0x%x", address,data);
NRF_LOG_FLUSH();
send_data();
}
NRF_LOG_FLUSH();
}

void send_data(void)
{
ret_code_t err_code;
uint8_t address = (0x54U);
uint8_t sample_data=0xaa;
uint8_t sample_data1;

err_code = nrf_drv_twi_tx(&m_twi, address, &sample_data, sizeof(sample_data), true);
//Wait for the transmission to get completed
//while (m_xfer_done == false){}
nrf_delay_ms(1000); // give some delay

// If transmission was not successful, exit the function with false as return value
if (NRF_SUCCESS != err_code)
{
NRF_LOG_INFO("FAILED 1.");
NRF_LOG_FLUSH();
}
else
{
NRF_LOG_INFO("SUCCESS 1.");
NRF_LOG_FLUSH();
}

}

This is my log on nrf module :- 

<info> app: TWI scanner started.
<info> app: TWI device detected at address 0x28...0x0
<info> app: SUCCESS 1.
<info> app: TWI device detected at address 0x54...0xAA
<info> app: SUCCESS 1.

0XAA is the data which I had sent to the slave. Now why is it scanning 2 addresses when I have attached only one slave with address 0x54?? 

[Kenneth]

I think I read somewhere that the ATSAMD20 can support multiple (e.g. 2) i2c slave addresses?

Kenneth

[sne_333]

Thanks, I got it. I had one question. I tested my code with SDA and SCL lines as p026 and p027. Now if I want to use SCL pin as P1.09 and SDA pin as P0.11 how do I configure port 1 and port 0 seperately?

[Kenneth]

You can use the following macro from nrf_gpio.h:

/** @brief Macro for mapping port and pin numbers to values understandable for nrf_gpio functions. */
#define NRF_GPIO_PIN_MAP(port, pin) (((port) << 5) | ((pin) & 0x1F))

e.g. scl = NRF_GPIO_PIN_MAP(1,9);

[sne_333]

Hi Kenneth,

         Thanks for your reply. I solved that issue. Now my question is I have 3 slaves connected to NRF52840 on the same I2C lines SCL pin as P1.09 and SDA pin as P0.11. I am able to connect to slave 1. Now for adding slave 2 and slave 3 do I need to add something extra or I can read all 3 slaves from the same instance?? 

Warm Regards,

Snehal.

[Kenneth]

Hi,

Good to hear you have solved it. There should be nothing in specific needed to handle 3 slaves, you only need to update the address for each slave, and also I suggest wait for the previous transaction to complete before starting the next.

Kenneth