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From: jgreco@archimedes.math.uwm.edu (Joe Greco)
Newsgroups: comp.sys.cbm
Subject: Re: C64 as printer buffer
Message-ID: <3832@uwm.edu>
Date: 7 May 90 14:29:06 GMT
References: <1990May2.234250.2626@uunet!unhd> <3760@uwm.edu> <1976@polari.UUCP>
Sender: news@uwm.edu
Organization: University of Wisconsin, Milwaukee
Lines: 26

In comp.sys.cbm article <1976@polari.UUCP>, tronix@polari.UUCP (David Daniel) wrote:
:>Not terribly difficult, except for one consideration:  there is only one
:>readily accessible parallel port on the 64 - the user port.  This means
:
:Not true. The User Port of the 64 is an RS-232 (ala CBM) I/O port.

I'd start disclaiming that statement; it's just not true.

The user port on PET/CBM/VIC/64/128 machines has traditionally been a
parallel 8-bit bidirectional I/O port.  On the VIC and I believe the PET
machines, this is implemented as a 6522 VIA.  On the 64 this is implemented
as a 6526 CIA.  Read the chip documentation; it'll tell you: "Parallel I/O".

Commodore, however, decided to add a little more functionality to the user
port on the VIC and (later) the 64.  They added software that allowed a
parallel port to mimic a logic level RS232 port.  This is one of the main
reasons that it was not implemented as a true RS232 port - you'd lose the
functionality of the User Port.

If you've seen some of the earlier parallel printer interfaces, they consist
of a specialized cable from the user port directly to a Centronics
connector.

In summary:  User Port is Parallel.  It just mimics serial.

... Joe