Question
I want to use the AD7793 in continuous mode. By using a 64 khz output from the
processor, I will perform a periodic interrupt procedure to read the AD-data,
without need to read the data ready information. Trying to calculate the
period, I find that 64000/470 is not an integer. Is the output repeated every
136 period, e.g. 470.58824Hz? Or is the 64 kHz upscaled in the circuit, then
what is the upscale factor and the number of periods at this higher frequency?
Answer
The sample rates quoted in the AD7793 datasheet are not exactly accurate. Each
conversion actually takes 0.125 ms longer than the value given in the
datasheet. So, for the 500 Hz update rate, the conversion time should be 1/500
+ 0.125 ms = 2.125 ms. This equates to 470.588 Hz. This occurs for all the
update rates. The values listed in the datasheet did not include this delay.
This method of synchronising the reads in continuous-read mode is not mentioned
in the datasheet but it will be interesting to see how it works out. I can't
see any reason why it shouldn't work.