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AD7760 bit problem

Question asked by numbersofpi on Feb 25, 2015
Latest reply on Mar 2, 2015 by jcolao

Hello, I am controlling the AD7760 ADC (on the evaluation board) with aNational Instruments' myRIO device. When I read out data bits, it seems mostly correct but there are some problems.  The datasheet specifies that the status bits will be sent out as 8 the LSBs of the second read, but they come out during my first read (consistently 10000000). Also, in the first read, the two MSBs are always 1, they never change with voltage levels. In the second read they vary between 1 and zero, and correctly vary depending on the voltage level, so I don't think it's an electrical problem. Otherwise the converted data bits seem to match up well with the voltage I'm applying.

 

My timing might be somewhat skewed from where it should be, so I'm trying to carefully go through the LabView code I wrote, but I haven't found any obvious errors, and it is 80% working, and it seems that if there is a timing problem it shouldn't work at all. I don't understand why a) status bits are in the wrong read, and b) bits 15 and 16 of first read are always on while everything else seems to behave well. Any trouble-shooting suggestions would be appreciated.

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