Experimental Physics and Industrial Control System
Subject: |
RE: Should ai, ao records have RAWH, RAWL? |
From: |
Stephanie Allison (415)926-4534 <[email protected]> |
Date: |
Wed, 9 Oct 1996 9:23:30 -0700 |
>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.
This sure would simplify ai device support for the Allen-Bradley
Direct Communication Module (1771-DCM) where the people writing
into the DCM promise they will always write unsigned 12 bit values,
except when they don't (oh yea, that's a 16 bit signed value...).
Instead of RAWH and RAWL, I'd prefer a MASK and SIGN field used by
device support in updating RVAL. In my case, MASK would be the
bits used (0x0FFF for a 12 bit value) and SIGN would be either
0/1 for unsigned/signed or a mask of the sign bit in RVAL. But this
probably goes too far toward the "unlimited set of configuration
fields" problem. No need to comment on this.
I assume that if RAWH and RAWL values change, a special SPC_LINCONV
will be done to get an updated ESLO (like is done when EGUF and EGUL
is changed).
Stephanie
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