M52233DEMO - ADC in differential mode

[GP]

Hi everyone,

I've a little question about the ADC module (using M52233DEMO board).

In single ended mode, everything's allright. The result of the conversion is correct, but in differential mode, when AN0 = AN1, AN2 = AN3, AN4 = AN5 and AN6 = AN7, all results are about 0x4008 instead of 0. Here's my registers values:

PANPAR = 0xFF; //All pins in AN mode

CTRL1 = 0x00F5; //Differential mode + Triggered + Parrellel

CTRL2 = 0x0023; //Simult + DIV (=/16)

ADLST1 = 0x3210; //Sample 0 = AN0, Sample 1 = AN1,...

ADLST2 = 0x7654;

ADSDIS = 0; //All samples enabled

POWER = 0x00D4; //Power up delay + Reference auto

CAL = 0; //Using VRH and VRL pins

Any idea ?

[macl]

I think what you're measuring is mid range when both inputs in the differential pair are equal.  To get a zero, the :smileyplus: input would be at VREFL, and the :smileyminus: input would be at VREFH.  With zero in the offset register, the result will always be positive. You can set the Offset register to give a signed result which will be zero when the pair is equal.