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<== Date ==> <== Thread ==>

Subject: Should ai, ao records have RAWH, RAWL?
From: LUCHINI@slc.slac.stanford.edu
To: tech-talk@aps.anl.gov
Cc: luchini@slc.slac.stanford.edu
Date: Wed, 9 Oct 1996 12:09:15 -0700
In response to the following:
> 
> Last week during a visit at DESY, Gabor Csuka
> suggested that the ai and ao records should have two additional
> fields RAWH and RAWL. The reason is that often it is possible
> to create common device support for a set of modules that differ
> only in the number of bits and/or polarity.
> 
> I expressed concern that this opens door to an unlimited
> set of configuration fields. After discussion I had to agree
> that these two fields  are generic enough that perhaps
> we should add them. They would not impact any existing support
> but future support could use them.
> 
> For example if a device is a bi-polar 12 bit adc the fields would
> be
> 
> RAWH 2047 RAWL -2048
> 
> If the device is a 14 bit unipolar adc the fields would be:
> 
> RAWH 16383 RAWL 0
> 
> Comments anyone?
> 
> Marty Kraimer

If adding RAWH and RAWL fields to ao and
ai record it would seem prudent to add a
field describing the conversion method
as well, such as two's compliment,
offset binary, or something else. 
You may also want to indicate how 0 in 
adc/dac counts is mapped (ie: RAWZ ), with
the default set to 0. 

I'm guessing that the original suggestion 
assumed a two's compliment method with 0
(amps or volts) mapped to 0 (adc/dac counts)
for a bipolar device.


    - Kristi Luchini
---------------------------------------------------------
Kristi Luchini  Internet  luchini@slc.slac.stanford.edu
SLAC            Voice     (415) 926-3417  



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