Experimental Physics and Industrial Control System
Subject: |
N.I. GPIB-1014 hack - was Granville-Phillips VG-307 vs GPIB |
From: |
[email protected] (Bill Brown) |
Date: |
Mon, 8 Aug 94 15:27:05 PDT |
We seem to have a work-around for the problems we had driving the VG-307 Vacuum
gauge controller with the N.I. GPIB-1014 vme interface. Those with weak stomachs,
as well as those subject to fainting or sudden attacks of the vapours, should not
read the rest of this post, as the subject matter may not be suitable for those
with weak constitutions.
A number of people on the list, including John Winans who wrote the driver and
device support, suggested that the problem may be due to timing. While it _may_
be possible to re-write the driver to operate in a polled mode, it's not clear
(to me) that this would eliminate all hardware timing dependencies.
The '1014 uses a chip manufactured by NEC (UDP7210) as an GPIB interface
controller. Once the DMA chip and the GPIB controller are set up and "fired,"
the GPIB protocol is generated by the hardware controller. Examination of the
prints show that the controller is clocked by a 8 MHz signal, derived from
the 16 MHz vme SYSCLOCK.
The board happened to be layed out such that the trace from the chip which
derived the 8 MHz clock to the UDP7210 clock input could be cut without
disturbing the rest of the 8 MHz clock distribution.
What we (shudder) did was to cut the trace and insert an additional 'ls161
counter, which generated a .5 MHz clock for the UDP7210. Since there are
no unused chip-sites on the board, the additional chip is installed "dead-bug"
fashion.
The modified board has been running since Friday morning with no problem.
Currently it is talking to two vacuum gauge controllers. Before the mod, one
or both of the controllers would usually wedge within an hour of operation.
It's possible that we could get by with a smaller divisor; perhaps things will
slow down and I can tinker with it a bit. It would be interesting to
understand where the controller is getting into a race condition, but I don't
think that I can spend much time reverse-engineering the vacuum gauge controller
interface.
It will be interesting to see if this mod also provides a solution to the problem
of the Digitel 500 Ion Pump Controller.
So there it is. It ain't very aesthetically pleasing, but it is fairly cheap
to do and it seems to solve the problem at hand.
"Beware of programmers bearing screwdrivers." -Anon.
Disclaimer: Any opinions are my own and have |
nothing to do with the official policy or the | -bill
management of L.B.L, who probably couldn't | [email protected]
care less about employees who play with trains. |
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