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ADS7828 reading problems

Other Parts Discussed in Thread: ADS7828

I'm using boundary scan to communicate with an ADS7828.  I'm getting strange results when I read back the last two converted data bytes.  I see on other posts that there may be an issue with the reference  if the wrong cap value is used.  Here are my conditions:

1.  Supply voltage 3.3V

2.  Using internal reference

3.  vref cap is 100nF

I've put in the recommended 'dummy' address byte and command byte to turn on the internal reference but I still get 0s.  I get ack signals back on all bytes that I send to the ADS7828. BTW i also occasionally get data but it is the same code out on multiple reads.  

Is there a min sclk freq for this device?  No min freq is stated, but with boundary scan, it's difficult to provide a 50% duty cycle.

Does anyone know what it means to read 0s or the same code repeatedly?  All other responses on the i2c bus from devices are correct.