How to implement RESET button on nRF51822?

RE: How to implement RESET button on nRF51822?

Håkon Alseth — Wed, 29 Jan 2014 12:10:09 GMT

Oh' sorry, did not answer the full post. There is no internal capacitor, other than the stray capacitances that you have in the pad connection and PCB tracks (totals <10 pF-area).

Best regards Håkon

RE: How to implement RESET button on nRF51822?

Håkon Alseth — Wed, 29 Jan 2014 12:07:06 GMT

It's a schmidt trigger. The internal pull up is ~47kOhm.

-H

RE: How to implement RESET button on nRF51822?

William Grange — Tue, 28 Jan 2014 20:34:31 GMT

Thanks, Paul. I will keep an eye out.

RE: How to implement RESET button on nRF51822?

Paul — Tue, 28 Jan 2014 17:26:57 GMT

Just be very careful that the reset trace from the button to the IC is not too long. nRF51 likes to pick up noises on the reset line.

If you have a long (more than 1 inch) reset line, you need to put a strong pull up (1K or 470) as close as possible to the IC (in less than 100mil distance). Layout is not a given.

I have raised this issue to Nordic a while ago. I guess I cannot say this is an issue, which is a common practice when you are dealing all other micros. Let's call it "Be Aware".

RE: How to implement RESET button on nRF51822?

William Grange — Tue, 28 Jan 2014 03:50:19 GMT

Hi Håkon,

I was planning to use an active-low reset switch in parallel to SWDIO just like Michal describes. The -EK shows 150Ω in series with the switch to ground.

Is the value of the pull-up 13kΩ similar to the GPIO?

Also, can you comment on whether there is an internal capacitor to GND on the reset line or a Schmidt trigger on the reset line's input to de-glitch the transitions?

Thanks, William

RE: How to implement RESET button on nRF51822?

Michal Zacharias — Thu, 19 Dec 2013 15:59:48 GMT

Thank you :)

RE: How to implement RESET button on nRF51822?

Håkon Alseth — Thu, 19 Dec 2013 15:58:38 GMT

Yes, that is correct. there's an internal pull up on that pin.

-H

RE: How to implement RESET button on nRF51822?

Michal Zacharias — Thu, 19 Dec 2013 15:27:20 GMT

So SWDIO/nRESET has internal pullup? I don't need to add hardware pullup? Just line from SWDIO/nRESET to programming header and parallel to it I should put an active low reset button?

RE: How to implement RESET button on nRF51822?

Håkon Alseth — Thu, 19 Dec 2013 15:04:58 GMT

Hi,

You can connect a button from SWDIO/nRESET, which is active low (ie, tied to GND when pushed). When the MCU is in normal run mode, the SWDIO/nRESET pin can be used a normal reset input.

When you program the nRF-device, it will run in "debug mode" until you do a power cycle or do a pinreset from the debugger (cmd line: "nrfjprog --pinreset")

Best regards Håkon