TWI example twi_master_with_twis_slave

[Sascha Schmidt]

Hello,

I'm using the TWI example mentioned in the subject line and I'm trying to get the TWI signals out of my demo board (Rigado BMD-350 Evaluation board).

Am I right that in this example the signals don't come out of the hardware pins because it's a simulated EEEPROM? How can I change the example to bring out the signals, so I can measure these?

Thanks in advance for any help!!!

Kind regards

Sascha Schmidt

[Håkon Alseth]

Hi Sascha,

 

There are a couple of more examples for TWI usage. You have the "twi_master_using_nrf_twi_mngr" which uses the TWI manager, then you have the "twi_scanner" and "twi_sensor" which accesses the nrf_drv_twi driver directly.

The GPIOs used for TWI can be altered in twi_init(), where the default is "ARDUINO_SCL_PIN" (GPIO 27) and "ARDUINO_SDA_PIN" (GPIO 26)

Examples enable the internal pull up resistor (13 kOhm nominal), which restricts the maximum bus speed to 100 kHz. If you need 400 kHz, then stronger external pull up resistors are required (3.3 kOhm for instance).

Kind regards,

Håkon

[Sascha Schmidt]

Hi again,

sorry my former description of the error was not completly correct:

the function nrf_twi_task_trigger(p_twi, NRF_TWI_TASK_STARTTX); set the ERRORSRC register in the controller in the function 'twi_tx_start_transfer', and than afterwards the 'twi_transfer' function abords the transmission.

As far as I understood the description in the info center the function nrf_twi_task_trigger should set the NRF_TWI_TASK_STARTTX bit in the hardware register? Is that correct?

If yes how can I correct that?

Kind regards

Sascha

[Sascha Schmidt]

Hi,

I have no slave connected, just a logic analyzer to see the signals and understand how the transmission works. I found the description for the ERRORSRC register in the datasheet of the chip. What I was wondering about was, why the function nrf_twi_task_trigger(p_twi, NRF_TWI_TASK_STARTTX) sets this ERROR register. Shouldn't it set the STARTTX bit?

Kind regards

Sascha

[Sascha Schmidt]

A line like this:

uint8_t sascha = offsetof(NRF_TWI_Type, TASKS_STARTTX); ///< Start TWI transmit sequence.

gives the result sascha = 8

Is that correct?

[Håkon Alseth]

When the TWI Master peripheral starts a transmission, it requires an acknowledge from the slave in order to continue. If this ACK is not received, it will set an event in the ERRORSRC register corresponding to the error detected.

Calling nrf_twi_task_trigger(p_twi, NRF_TWI_TASK_STARTTX) is the equivilant to calling NRF_TWIMx->TASKS_STARTTX=1, which will tell the hardware peripheral to start the communication towards the TWI Slave device. The ERRORSRC is set as no one is pulling the line low (creating a ACK) at the end of the transmission.

I'd recommend that you read up on how the TWI (or I2C as its more commonly named) works on a bus level to get to know the protocol a bit better.

 

Kind regards,

Håkon

[Sascha Schmidt]

Now I've got it :) The two TWIs have to be physically connected, otherwise the example won't work. Many thanks for your help!!

Kind regards

Sascha

[Sascha Schmidt]

Just another short info to the example. It won't work unless the UART RX Buffer size isn't corrected. In the example the buffer size is defined with 16byte. This is too less. The buffersize has to be increased otherwise the example won't work correctly.

Kind regards

Sascha