I'm having a problem with the nRF52 SAADC. It's configured for
- One shot operation on Channel 0 using pin Ain4.
- Gain of 1/6
- Tacq set to 40us
- 8 bit resolution
- Internal reference
- Single ended (PSELN connected to ground)
- No oversample
- burst disabled.
- Sample rate controlled from task
Here's the contents of my "read" function:
uint16_t sample;
NRF_SAADC->RESULT.PTR = uint32_t(&sample);
NRF_SAADC->RESULT.MAXCNT = sizeof(sample);
NRF_SAADC->EVENTS_STARTED = 0;
NRF_SAADC->TASKS_START = 1;
while(NRF_SAADC->EVENTS_STARTED ==0){nop();}
NRF_SAADC->EVENTS_DONE = 0;
NRF_SAADC->TASKS_SAMPLE = 1;
while(NRF_SAADC->EVENTS_DONE ==0){nop();}
NRF_SAADC->EVENTS_STOPPED = 0;
NRF_SAADC->TASKS_STOP = 1;
while(NRF_SAADC->EVENTS_STOPPED ==0){nop();}
I have the Ain4 pin connected to ground through a 200 ohm resistor. Is it possible for the ADC to return negative when it's configured for single ended and the analog input goes lower than ground?
