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From: jhs@MITRE-BEDFORD.ARPA
Newsgroups: net.micro.atari8
Subject: Re: bidirectional ST printer port
Message-ID: <8604021848.AA11023@mitre-bedford.ARPA>
Date: Thu, 3-Apr-86 07:28:50 EST
Article-I.D.: mitre-be.8604021848.AA11023
Posted: Thu Apr  3 07:28:50 1986
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I'm not an ST owner but I will speculate that the printer port is a standard
"PIA" or 68000-family equivalent.  (Actually they may well use the 6800 family
chip, as it ought to be entirely compatible.)  If so, the same wires are both
an input and an output.  Also, the device control register information can be
looked up in a standard PIA data sheet and you will be able to figure out how
to program it to be an input.

On the 800XL, the joystick ports are the same way.  They are tied to a PIA and
are usually used for input.  But they can just as well be written to as
outputs for special purposes - like hooking up a parallel printer without
paying for an expensive interface!

-John Sangster
jhs@mitre-bedford.arpa