Re: DEC AXV11-C analog board

[Paul Koning via cctalk]

> On Feb 8, 2022, at 2:34 PM, Douglas Taylor via cctalk <cctalk@classiccmp.org> 
> wrote:
> 
> Update on this:  I did put together a battery and voltage divider to test the 
> AXV11.  The label on the A/D module says it brings the output from the 
> multiplexer to one of the external pins.  I was able to verify that the 
> voltage applied to a couple of the A/D inputs makes it through the 
> multiplexer when selected using the CSR.  The next output available is from 
> the Sample and Hold, and this is always pegged at +12v.  Am I wrong to assume 
> that the sample and hold will 'freeze' its output when the A/D go bit is set?

You're correct, a S/H circuit is supposed to hold the value that was on its 
input at the time it was told to take the sample.  Typically it won't hold it 
"forever"; S/H circuits have a hold time spec chosen so it is substantially 
longer than the time it takes the A/D behind it to complete its measurement.

        paul