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From: grr@cbmvax.UUCP
Newsgroups: comp.sys.atari.st
Subject: Re: Parallel printer port problem
Message-ID: <1078@cbmvax.cbmvax.cbm.UUCP>
Date: Wed, 10-Dec-86 02:37:55 EST
Article-I.D.: cbmvax.1078
Posted: Wed Dec 10 02:37:55 1986
Date-Received: Sun, 14-Dec-86 00:07:59 EST
References: <861208225517.00000698.ATCV.MA@UMass>
Reply-To: grr@cbmvax.UUCP (George Robbins)
Organization: Commodore Technology, West Chester, PA
Lines: 33

In article <861208225517.00000698.ATCV.MA@UMass> LSI@UMass.BITNET (Peter Lawall, Logical Solutions, (413) 256-6800) writes:
>Rick Flashman (Flash%UMass.BITNET@WISCVM.WISC.EDU) writes:
>
>>     BTW, Atari's Printer port on the ST is NOT all that STANDARD. If you
>> are trying to hook a Okidata dot-matrix printer to an ST, talk first to
>> your local Atari dealer. There are cable modifications that must be made
>> cause Atari did not use a standard connection....some voltages are
>> messed up or something. Need a tech for that one.
>
>   The only technically "non standard" thing about the parallel printer port
>is that it only supports BUSY handshake as opposed to both BUSY and
>ACKNOWLEDGE.  This isn't usually a problem, as every printer that I know of
>provides a BUSY output in addition to the ACK output.
>
>                                 Peter

It should perhaps be pointed out that not many micros, nor many micro printers
really conform to the real Centronics 'standard'.  This however, doesn't keep
most of them from inter-operating, although there are these occasional problems.

Specifically, the Centronics 101A manual required ~15mA drive on the data and
control lines.  Not too many NMOS chips can do this reliably.  There are also
a bunch of relatively useless or partially redundant signals that most people
don't bother with. 

Also, as Peter mentioned you can do handshaking on either BUSY or ACK, but
on some printers you may find some performance degredation if you choose the
wrong one, due to buffering techniques and the relation of BUSY to the actual
printing action.
-- 
George Robbins - now working for,	uucp: {ihnp4|seismo|rutgers}!cbmvax!grr
but no way officially representing	arpa: cbmvax!grr@seismo.css.GOV
Commodore, Engineering Department	fone: 215-431-9255 (only by moonlite)