ADC1, ADC2 dual mode with differential input

[CyberNerd]

ADC1 and ADC2 run in interleaved dual mode using DMA. Resolution for both ADCs is set to 8-bit. ADC1 is sampling CH1 and CH2 in differential mode. The results that I get from DMA are a bit strange: 

If my positive input is ~1.65V, if my negative input is also ~1.65V, I get 127 counts? What am I missing here? I would expect that if there is a small pos or neg difference, value will be close to 0 instead of close to 128.

[waclawek.jan]

 

(Adjusted for the 8-bit setting, of course.)

JW

 

 

[CyberNerd]

Assuming 12-bit resolution, to get the voltage you need to do this: