AD7858: Channel Switching and Software Conversion

Document created by analog-archivist Employee on Feb 23, 2016
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I am programming bean for AD7856 and AD7858. I would like to known why two
separate writes are required to set a new channel address and initiate
conversion on that new channel in software for AD7858 and not for AD7856. (Data
sheets page number 27)

 

AD7858
When a change of channel and convert start command are both contained in single
write operation to the control register,
1.  the input multiplexer is changed first
2. and then the conversion is started.
In other words the new conversion is carried out on the channel you have just
selected. This does not leave sufficient settling time for the newly selected
channel, and so the conversion result will be garbage. Therefore we recommend
two separate write operations, to allow sufficient settling time and
acquisition time after the MUX has switched.

AD7856
When a change of channel and convert start command are both contained in single
write operation to the control register,
1. the conversion is started first, on the previously selected channel,
2. then the input MUX is switched to the new channel,
To convert on the channel you have just selected, you must sent another start
convert signal.

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