nRF52840 UART Transition Issues

RE: nRF52840 UART Transition Issues

BAEE — Wed, 25 Sep 2019 12:01:05 GMT

Thank you.

RE: nRF52840 UART Transition Issues

Einar Thorsrud — Wed, 25 Sep 2019 08:06:45 GMT

Yes, calling nrf_drv_clock_hfclk_request() starts the 64 MHz oscillator, which uses the 32 MHz crystall.

RE: nRF52840 UART Transition Issues

BAEE — Tue, 24 Sep 2019 17:28:35 GMT

Can you please tell me exactly which crystal/oscillator this selects on the schematic?

RE: nRF52840 UART Transition Issues

Einar Thorsrud — Tue, 24 Sep 2019 11:52:58 GMT

I am glad to hear that worked. And thank you for the detailed update! Such updates can be very useful for others when looking for a solution to a similar problem.

RE: nRF52840 UART Transition Issues

BAEE — Mon, 23 Sep 2019 15:52:07 GMT

OK, so we were finally able to select the XTAL as the clock source and everything works great. The following code was added to the config file to accomplish this.

#ifndef NRF_CLOCK_ENABLED

#define NRF_CLOCK_ENABLED 1

#endif

#ifndef NRFX_CLOCK_CONFIG_IRQ_PRIORITY

#define NRFX_CLOCK_CONFIG_IRQ_PRIORITY 6

#endif

#ifndef NRFX_CLOCK_CONFIG_LF_SRC

#define NRFX_CLOCK_CONFIG_LF_SRC 1

#endif

The following code was added to the main file:

nrf_drv_clock_init();

nrf_drv_clock_hfclk_request(NULL);

RE: nRF52840 UART Transition Issues

BAEE — Mon, 23 Sep 2019 13:24:03 GMT

Thanks, we will try that.

RE: nRF52840 UART Transition Issues

Einar Thorsrud — Mon, 23 Sep 2019 13:02:47 GMT

Then it looks like you need a more accurate clock source on the nRF. The cleanest approach would probably be to use the clock driver and call nrf_drv_clock_hfclk_request().

RE: nRF52840 UART Transition Issues

BAEE — Mon, 23 Sep 2019 12:44:42 GMT

On further investigation, it seems that the Nordic is running at 116504 baud even though we have it set to 115200. The other MCU is running at 115163 baud.

RE: nRF52840 UART Transition Issues

BAEE — Mon, 23 Sep 2019 12:26:05 GMT

We tried that but it seemed to make no difference.

RE: nRF52840 UART Transition Issues

awneil — Mon, 23 Sep 2019 12:17:03 GMT

Sounds like a bug in the other MCU - a UART should be sampling at the centre of the bit ...

Are you doing a software (bit-banged) UART on the other MCU ... ?

RE: nRF52840 UART Transition Issues

BAEE — Mon, 23 Sep 2019 12:14:37 GMT

The problem seems that when going from example a 0 to a 1, the transition happens right on the boundary of when the other MCU is determining the value of the 0 bit position. Sometimes, the other MCU recognizes the bit as a 0 and sometimes it recognizes it as a 1 because the value transitioned to the 1 a little early. I have connected two of the other type of MCUs and they always work correctly.

RE: nRF52840 UART Transition Issues

awneil — Mon, 23 Sep 2019 12:05:02 GMT

It's still not clear what, exactly, your problem is!

[quote userid="82088" url="~/f/nordic-q-a/52434/nrf52840-uart-transition-issues/211227"]the crystal oscillator[/quote]

Which one - on the nRF, or on the other MCU.

UART comms requires that both sides of the link have accurate clocks.

RE: nRF52840 UART Transition Issues

BAEE — Mon, 23 Sep 2019 11:57:21 GMT

I also believe it may be that the clock drifts too much between devices. However, unless we did something wrong, we attempted to select the crystal oscillator and it didn't seem to help the problem. Do you have some instructions for selecting the crystal oscillator?

RE: nRF52840 UART Transition Issues

awneil — Mon, 23 Sep 2019 11:52:49 GMT

[quote userid="82088" url="~/f/nordic-q-a/52434/nrf52840-uart-transition-issues"]the transitions happen too quickly[/quote]

What do you mean by that?

How about posting you LA screenshot to show what you mean?

How do you know it's the nRF being "too quick" - rather than other MCU being "too slow" ?

Or a bit of both?

RE: nRF52840 UART Transition Issues

Einar Thorsrud — Mon, 23 Sep 2019 11:30:43 GMT

Hi,

I am having problems understanding how "transitions happen too quickly", but it makes me think that you are talking about a situation where there are timing problems so that sampling happens too late, or similar? If so, I suspect one of two problems:

you have not configured the same baud rate in both devices, or
the clock drifts too much between the devices. For instance, you should consider enabling the crystal oscillator, since the RC oscillator may not be accurate enough (at least with high baud rates).

RE: nRF52840 UART Transition Issues

Nguyen Hoan Hoang — Sat, 21 Sep 2019 16:38:37 GMT

try enabling pullups.