Subject: |
Re: Infrequent I/O hardware |
From: |
[email protected] (Steve Lewis) |
Date: |
Mon, 28 Nov 94 09:23:52 PST |
One advantage of A-B (and its competitors, like Modicon) is that not
only are a wide range of input conditioning circuits available, but
generally clever packaging allows cards to be replaced with out
fussing with wiring. There is no hassle about front and back panels,
and everything is brought to screw terminals. The mounting styles for
the enclosures allow a lot of choices and meet most electrical/fire
codes. For A-B, we also find the freedom to locate the terminating
wires independently from the VME (or VXI or CAMAC) an advantage in many
situations. You can also put many "rack frames" on a single serial
line driven by one VME scanner, and they may all be dispersed quite a
distance.
As Chip mentions, there is a speed disadvantage, since the A-B scanner
polls at a relatively slow rate, about 10ms as I recall. For new
installations with modest speed requirements and any sort of ruggedness,
I would choose it. We used it here for the Bevatron and also for
Gammasphere.
We originally encountered some assumptions about even/odd addressing
built-in to the A-B drivers in EPICS that were no longer applicable for
later models, and Dalesio and his group were able to fix them very
quickly. The experience and support from LANL gives A-B a definite edge
over direct competitors (Modicon, Siemans). However, if you choose
similar hardware to CEBAF you will also get very strong support.
Steve Lewis
LBL
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