SPIM - MISO connection has very low level

RE: SPIM - MISO connection has very low level

bjorn-spockeli — Tue, 16 May 2017 11:14:11 GMT

The SPI driver in the SDK (nrf_drv_spi.c) will configure the CS pin so that its active low, see this Infocenter page. Quoting the documentation:

Slave Select pin number: Set to NRF_DRV_SPI_PIN_NOT_USED if this signal is not needed. The driver supports only active low for this signal. If the signal should be active high, it must be controlled externally. So in your case you will have to use the GPIO abstraction(nrf_gpio.h) abstraction to control the CS pin.

RE: SPIM - MISO connection has very low level

uC_newbie — Mon, 15 May 2017 21:33:33 GMT

Hey Bjorn,

thank you very much for your reply! i was able to resolve my issue and it was apparently due to the SPI-configuration pulling /CS up at points where the ADS1256 needed it to be low for a correct data transfer. i tied /CS permanently down to GND (as i only communicate with the ADS via SPI) and everything is working as intended. actually quite a malicious behaviour as it looked like a grounding issue.

but im curious: I used the SPIM example from the DK as a basis for my code. how does nrf52832 change the /CS during communication? when is chip select turned up? maybe i just have not understood the SPI protocol correctly yet.

RE: SPIM - MISO connection has very low level

bjorn-spockeli — Mon, 15 May 2017 12:50:59 GMT

So the ADS1256 is a breakout board that you connect to a custom nRF51/52 board? Have you been developing on one of our DKs?

RE: SPIM - MISO connection has very low level

uC_newbie — Fri, 12 May 2017 14:28:26 GMT

Hi, thanks for your reply.

i checked every ads1256 pin and all voltage levels are correct except for the MISO pin. because the observed phenomenon switches with the programming of the MISO pin i dont believe this is hardware related.

RE: SPIM - MISO connection has very low level

bjorn-spockeli — Fri, 12 May 2017 11:11:16 GMT

It sound like you have a power issue or that the MISO pin is pulled down through a short somewhere. Could you verify that the supply voltage to the ADS1256 and that there isnt any shorts?