Problem using digital IO as MISO.

RE: Problem using digital IO as MISO.

Luccas — Mon, 12 Aug 2019 14:25:55 GMT

I end up using the 100 ohms resistor in series. But I remember that ADC pins also worked as well.

RE: Problem using digital IO as MISO.

nataddrho — Sat, 10 Aug 2019 03:51:53 GMT

Have you found a good pin to use for MISO? Adding the 100 ohm resistor is EXACTLY what I did on my own independently before reading this thread, so I feel better. Maybe it is something weird with ST devices? It shouldn't be.

Lucas which pins did you end up using?

RE: Problem using digital IO as MISO.

RK — Sat, 01 Jun 2019 02:27:24 GMT

from your oscilloscope traces it looks like the signal was ringing badly; adding a resistor into the signal line better matches the output pin impedence (which is low) to the input one (which is high). If you google 'signal line current limiting resistor' you'll see it's occasionally recommended although I've very rarely ever had to do it. We have a PPS timing box with a very sharp accurate pulse and accurate 50 ohms output, if you don't match the receiver to that at least fairly well, it rings like crazy. 100 ohms sounds quite high, usually 20 or so does the job, add too much and you start to drop your own signal voltage.

RE: Problem using digital IO as MISO.

awneil — Fri, 31 May 2019 10:55:09 GMT

[quote userid="13562" url="~/f/nordic-q-a/47335/problem-using-digital-io-as-miso/187439"]The signal seems to struggle to pull the miso line high[/quote]

Indeed.

Something similar here:

https://devzone.nordicsemi.com/f/nordic-q-a/47968/spi-doesn-t-work-in-nrf52810-while-emulating-nrf52810-in-nrf52832dk-was-successful/190230#190230

(that's on an nRF52810)

RE: Problem using digital IO as MISO.

haakonsh — Wed, 22 May 2019 07:27:05 GMT

That's strange how a 100ohm series resistor fixed the issue.
Anyways I'm glad you fixed your problem, SPI can be a real b**** to debug xD

RE: Problem using digital IO as MISO.

Luccas — Tue, 21 May 2019 13:06:28 GMT

Haakonsh thanks for your support!

Actually I've also used the sensor and the nrf52 on our developed integrated board and the results were the same. I've accidentally discovered one solution, inserting some resistance(like 100 ohms) between the nrf pin and the sensor pin solved this strange behavior. Not sure why.

I've already used others sensors without this problem, so this must be something with this sensor.

RE: Problem using digital IO as MISO.

haakonsh — Tue, 21 May 2019 07:27:44 GMT

Serial interfaces can behave a bit strangely when using jumper wires between devices. The problem almost always goes away once you get both device on the same board. For now I suggest you try different I/O pins and use whatever works.

RE: Problem using digital IO as MISO.

Luccas — Thu, 16 May 2019 15:30:04 GMT

I've also tried that.

RE: Problem using digital IO as MISO.

Luccas — Thu, 16 May 2019 15:29:37 GMT

Yes, I've tried another digital pin with same results. Using AIN pin worked, but I dont know why.

RE: Problem using digital IO as MISO.

haakonsh — Thu, 16 May 2019 08:09:47 GMT

Have you tried using another pin? That pin's trace might have to much capacitance to be used for SPI.

RE: Problem using digital IO as MISO.

haakonsh — Thu, 16 May 2019 08:07:21 GMT

The signal seems to struggle to pull the miso line high. Have you tried using a pull-up?

ie. "NRFX_SPIM_MISO_PULL_CFG 3" // NRF_GPIO_PIN_PULLUP

RE: Problem using digital IO as MISO.

Luccas — Wed, 15 May 2019 18:05:06 GMT

Yes, It has the LED4 connected, I've already cut the SB8 connection to disable the LED.

RE: Problem using digital IO as MISO.

awneil — Wed, 15 May 2019 15:54:30 GMT

Have you checked the PCA10040 schematics to see if there's anything else connected to that pin ... ?