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From: krowitz%richter@UMIX.CC.UMICH.EDU (David Krowitz)
Newsgroups: comp.sys.apollo
Subject: Re: Adding Centronics Port to DN3000
Message-ID: <8912011429.AA03847@richter.mit.edu>
Date: 1 Dec 89 14:29:47 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
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To clear up a few things ...

A IBM-PC/XT compatible parallel printer port is fairly easy to
add to a DN3xxx/4xxx. The Apollo Serial/Parallel Expansion card
(the SPE) has such a port built into it. If your print-server
supports the SPE card, it will also work with the XT card -- they
are hardware compatible. The driver software for the SPE may be
another matter. You *definitely* don't want to drive the XT card
(or the SPE) with interrupts turned on. Processing an interrupt
for every single character sent will severely degraded the
performance of the CPU. You want to use programmed I/O which (although
it sits in a loop eating up CPU time waiting for the printer to
accept the next character) will not degrade the performance of
the other processes on the node. If I/O performance is a big issue,
get the Ikon 10092 or 10097 parallel printer boards with DMA
capability.

The DN3000 only has a single serial port. The special cable 
adaptor which gives 3 serial ports works only on the DN3500, the
DN4000, the DN4500, and the new DN2500. Adding extra serial lines
via an add-in board is a pain. The software is much more complicated
than for the parallel port. You'd be better off with one of the
supported products from someone like Danford, Workstation Solutions,
et-al.


 -- David Krowitz

krowitz@richter.mit.edu   (18.83.0.109)
krowitz%richter.mit.edu@eddie.mit.edu
krowitz%richter.mit.edu@mitvma.bitnet
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