Help me understand TWI/M and its API

[doryhealth]

Hello everyone

I'm doing my first steps so as to get things right from the start with a device based on the nRF52833 chip.

My setup: PC <USB> nRF52840-DK <JTAG> CustomBoard (nRF52833)

I am struggling to understand the TWI workflows and keep getting hard faults

Can one of you good people confirm or infirm the following points:

1) the functions nrf_drv_twi_tx or nrf_drv_twim_tx carry out an entire Master write sequence:

START, Address, 0W, (slave_ACK) - data[0] - (slave_ACK) - data[1] - (slave_ACK) .....- STOP

2) the functions nrf_drv_twi_rx or nrf_drv_twim_rx carry out an entire Master read sequence:
START, Address, 0W, (slave_ACK) - (slave_data) - NACK - STOP

3) To e.g. read a register, I have to write
- a tx function (sensor address, which register to be read)
- a rx function (sensor address, data from register defined in tx query)

Is this correct? In the sensor's datasheet (APDS-9603-065), the flow does not include a "break", i.e. NACK + STOP, for a register read.


Thank you, in advance, for the precious help

Jerome

[Jared]

Hi,

1. Correct
2. Correct
3. Looking at the part of the datasheet that you included this seems very correct. If you're using the twi driver then you can either do a nrf_drv_twi_tx() with the no_stop parameter as true, and then follow with a read with nrf_drv_twi_rx(). Or you can do both with one function call nrf_drv_twi_xfer(). Similar functions are available for the TWIM driver. 

Also, try probing the SCL and SDA line with a oscilloscope or a logic analyzer and see if the correct data is outputted from the nRF. 

regards

Jared