I am having an issue getting the AD7859 to consistently perform a full self-calibration.
AVDD and DVDD are at 5V with a stable external 5V reference.
My clock is running at about 3.75MHz.
I do not see any activity on the CS.
About 1 out of every 25 times, when I pull the /CAL pin low for 10us and then release it back to 5V I do not see the BUSY line go high.
Because of this when my software goes to perform its first conversion, the chip does a calibration and my conversion fails.
Is there any documentation of using the /CAL pin to perform the full self-calibration as the datasheet only full explains using the /CONVST pin?
What are the potential reasons the full self-calibration did not start when the /CAL pin was taken from low to high?
Thank you for your reply. However, I am not using the registers to initiate the calibration. I am using the /CAL pin (pin number 16 on the AD7859AS). From page 7 of the datasheet: "Calibration Input. A logic 0 in this pin resets all logic. A rising edge on this pin initiates a calibration. This input overrides all other internal operations."
My clock is 3.75MHz, which should give a calibration time of about 33ms.
My external reference is stable.
I pull the /CAL pin low for 10us, and then set it back high.
Most of the time I get a 33ms pulse on the BUSY (passing calibration).
Sometimes I do not get a BUSY pulse at all, and sometimes I get a BUSY pulse of about 100ms (which indicates a failed calibration).
I need to know what could cause a calibration to fail.
And I need to know what would cause a calibration not to start from the /CAL pin.