Unexplainable ADC values on LPC1769?

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 15, 2016 by lpcware
Content originally posted in LPCWare by Darko8 on Sun Apr 15 14:12:23 MST 2012

I'm using all 8 analog CH on LPC1769 ADC by selecting one by one. ADC is running on 12MHz (96MHz system clk divided by 8, and I tried other dividers also).

All analog values are defined with 10k potentiometers directly tied to power supply and if I leave them on some value I can read almost exact values with some small noise present, but every now and then I read 0xF700 to 0xFFF0 on some ADC channel or even very close to 0x0000.
I measured DC level with oscilloscope and it looks OK, without any apparent spikes.

I'm noticing those spikes only when debugging (with RedProbe+ debugging tool OR LPCXpresso link) and SWD is running, if the cable is only connected and firmware is running without debugging then all is OK.

I'm using CMSISv2 and I start AD conversion with or without 100us waiting after AD channel selection. I'm using ADC in single conversion mode by using command ADC_START_NOW.

Any ideas of what could cause such random ADC conversion anomalies while debugging?

Best regards, Darko Obretan