P0.08 not working with nRF51822 QFAC

[Guillaume Levant]

Hi,

I have a PCB with a nRF51822 QFAC A1 onboard, and I wrote a firmware with mbed for this PCB in which P0.08 is supposed to be set to 1 during the initialization and is never set to 0 after. But when I test the firmware this GPIO is always at 0. I tried to find a short circuit but according to my multimeter the resistance betwen p8 and Vss is 33kOhms, which is correct according to the schematic of my PCB. Is this pin has a specific function and could not be set to 1 ? I didn't find any information confirming this in the datasheet.

I use softdevice s110 7.3.0

Best regards,

Guillaume

[MartinBL]

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.

[Guillaume Levant]

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
}

[MartinBL]

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?

[Guillaume Levant]

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.

[Guillaume Levant]

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