SAM4E AFEC in differential mode

larryk Guest 2014-04-23 09:54 #3627424

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Hi all,

I try to use the SAM4E AFEC in differential mode. The use of the offset 
in this mode is not clear to me. Main question is, does the offset in 
diff mode only affect the common mode setting or is it applied to the 
differential result.
My recent triees to use the offset had no effect to the AFEC output 
value.

Some details on the setup:
ADVREFP = 2.73V
AD8131 to drive the diff input +AD4/-AD5
common mode voltage is 1.36V
The AFEC is centered (2048) for AD4 = AD5 what equals 0V input for the 
AD8131. My initial intention was to use the offset to move the AFEC zero 
to 0V input voltage.

I tried various ways, with AFEC_CDOR as well as AFEC_COCR. For channel 4 
as well as for channel 0 depending on ANACH. To the best of my knowledge 
the calibration routine is also called.

Thanks for your time, Larry.

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larryk Guest 2014-04-24 13:47 #3629131

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Ok, digidal offset compensation is not supported in diff mode. I 
received a reply from ATMEL support:

The offset compensation is not available in differential mode, this is
only for single ended mode. The signal will be centered to 1/2*ADVREF by
default.

Datasheet section 43.6.9 :
    "The Offset is only available in Single Ended Mode."

Don't know why I haven't seen this I spent several hours with debugging 
and the datasheet.

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