IO expander control with TWI

RE: IO expander control with TWI

MartinBL — Tue, 23 Feb 2016 15:08:38 GMT

Glad it works! Updated my answer a little bit with some additional details.

RE: IO expander control with TWI

Anunnaki — Tue, 16 Feb 2016 16:36:51 GMT

I have changed the reset pin to an other pin, and the address to 0x20 (shift left was not necessary) and everything works!

thank you!

RE: IO expander control with TWI

Anunnaki — Tue, 16 Feb 2016 13:51:23 GMT

Hello,

Yes, I understand that the P0.21 is chip reset pin. However, I can't change the TWI pins.

Do i have to specifically instruct that that pin is not used as reset? If yes, how? And if that would be the issue wouldn't the chip just reset when i try to write something?

Thank You! Regards

RE: IO expander control with TWI

MartinBL — Tue, 16 Feb 2016 13:29:43 GMT

First, pin 21 on the nRF52 is a chip reset pin unless otherwise is configured in the UICR->PSELRESET registers. So if possible try to use a different set of TWI pins.

Second, when you don't provide an event handler function to nrf_drv_twi_init() the TWI driver will operate in blocking mode. I.e. if something goes wrong your application will get stuck in nrf_drv_twi_tx(). In this case the blocking mode is probably not the issue though, but the pins that you use might be.

Edit: When a pin is configured as a reset pin it is disconnected from other functionality, so your chip won't reset whenever the TWI is active. What I think happens in your case is that: The SCL signal is routed to the reset pin, but the reset functionality overrules the TWI functionality. Hence, the TWI transaction fails and since you have configured the TWI module in blocking mode the code hangs in nrf_drv_twi_tx().