Table VI. Calibration Truth Table
Cal Type * MD2, MD1, MD0 * Zero-Scale Cal * Full-Scale Cal
Self-Cal 0, 0, 1 Shorted Inputs VREF
System Cal 0, 1, 0 AIN
System Cal 0, 1, 1 AIN
System Offset Cal 1, 0, 0 AIN VREF
Background Cal 1, 0, 1 Shorted Inputs VREF
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using its zero scale cal commands i can not null for example an 30 mv dc input voltage

using its full scale cal commands, for example its Vref (2476 mv) ones, the read out go a saturated number such as $AAAB12 (rarely i see $ffffff) for voltage more than about 2000 mv ???

i expect to see $ffffff for Vin >= Vref
i expect to see $000000 after zero scale calibration for Vin ~ 30 milivolts
i do the proposed calibration according to the datasheet 1st step: zero scale cal & 2nd step: full span cal