jose orlando t. ribeiro wrote:
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the memory cell may fail 0->1 but not 1->0)

I had a different but somewhat similar problem - with DAC, if I was switching it to a voltage far away from previous value, (i.e. from 000 to fff with 12-bit DAC) it wasn't getting all the way there, output readout showing some 90%. Only setting it TWICE actually brought it to desired value.