P0.08 not working with nRF51822 QFAC

RE: P0.08 not working with nRF51822 QFAC

Peter Kmet — Mon, 12 Dec 2016 11:28:35 GMT

Same problem here with mBED code and P0.08. Looks like some library code takes over the pin, like Serial, etc. Now investigating.

Port p8 is multiplexed with UART RTS signal. What helped to me was to disable hardware flow control.

RE: P0.08 not working with nRF51822 QFAC

Guillaume Levant — Fri, 03 Jun 2016 07:52:59 GMT

P0.09 (the BTN pin) is connected to an internal pull-down resistance, could this cause a problem ?

RE: P0.08 not working with nRF51822 QFAC

Guillaume Levant — Wed, 01 Jun 2016 08:09:03 GMT

I agree but when I keep the button pressed and check the state of p0.08 with a voltmeter or even with eclipse while debugging, it is still low even after the initialization. It seems like the GPIO cannot be set to 1 or is always reset to 0, but I can't see the reason.

RE: P0.08 not working with nRF51822 QFAC

MartinBL — Wed, 01 Jun 2016 08:00:40 GMT

I guess that if the TPS79933 and/or the nRF51 turn off when the button is released it is no wonder why you don't measure any significant voltage on P0.08. Maybe the voltage regulated by the TPS79933 of some reason dips just long enough for the nRF51 to power down and "release" P0.08. If that is the case then maybe a bulk capacitor can help filter out the dip and solve the problem. It is hard to tell what's wrong.

RE: P0.08 not working with nRF51822 QFAC

Guillaume Levant — Mon, 30 May 2016 15:20:18 GMT

Yes it is exactly how it is supposed to work

RE: P0.08 not working with nRF51822 QFAC

MartinBL — Mon, 30 May 2016 13:06:06 GMT

So:

The BTN net and P0.09 acts as some sort of pin interrupt?
Your plan is to push the button which will turn on the LDO. The LDO in turn turns on the nRF51, which then pulls P0.08 high to keep the LDO on after the push button is released?

RE: P0.08 not working with nRF51822 QFAC

Guillaume Levant — Mon, 30 May 2016 10:32:16 GMT

Hi, I didn't have any news so far, is there anyone who can tell me how to solve this problem ?

RE: P0.08 not working with nRF51822 QFAC

Guillaume Levant — Wed, 25 May 2016 12:53:35 GMT

U8 is a TPS79933 from Texas Instruments, the VIH is 1.2V. When P8 is high (at 3.3V), the EN pin voltage of the TPS79933 should be 2.2V, which is sufficient to keep it enabled. The problem is that when the button is released the device turns off, and when I measure the voltage at p8 with a multimeter I have around 20mV (with the button pressed). I tried to read the output of P8 while debugging, and it is always set to 0, despite the fact I set it to 1.

RE: P0.08 not working with nRF51822 QFAC

MartinBL — Wed, 25 May 2016 12:43:26 GMT

How exactly do you know that the pin is always at zero? Have you measured the voltage with a multimeter or do you just assume it is always zero because EN on U8 is never high? Without knowing what U8 is, it seems strange to me that you have a button that when activated connects U8-EN to 4.1V, and yet you have a voltage divider from the nRF51 EN-net dividing the pin voltage down to two thirds of the nRF51s supply voltage, which I assume is 3V3?

RE: P0.08 not working with nRF51822 QFAC

Guillaume Levant — Wed, 25 May 2016 08:56:24 GMT

Hi, Thanks for your quick answer. The part of the schematic is the following : www.hostingpics.net/viewer.php The EN net is connected to P0.08, BTN net is connected to P0.09 which is connected to an internal pulldown resistance. The switch is a pushbutton to turn on the LDO, which should be maintained on by P0.08

The code is the following :

DigitalOut LDO(p8);

int main()
 {
	LDO = 1;
//rest of the main
}

RE: P0.08 not working with nRF51822 QFAC

MartinBL — Wed, 25 May 2016 08:30:19 GMT

Hi,

The pin should not have any special function. I assume it is a completely custom board? Not just something that is hooked to a development kit?

Are you using any other hardware modules, like e.g. UART, that might be configured to use pin 8 by default?
Do you mind posting your schematic, layout, and code showing how the pin is configured and tested?

The pin assignments are documented in the Product specification.