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From: stergios@rocky.UUCP
Newsgroups: comp.sys.amiga
Subject: Parallel port direct access
Message-ID: <236@rocky.STANFORD.EDU>
Date: Wed, 15-Apr-87 14:59:25 EST
Article-I.D.: rocky.236
Posted: Wed Apr 15 14:59:25 1987
Date-Received: Sat, 18-Apr-87 01:06:52 EST
Reply-To: stergios@rocky.stanford.edu (Stergios Marinopoul)
Distribution: world
Organization: Stanford University Computer Science Department
Lines: 38


	I'm trying to figure out how to access the parallel port directly
through hardware, rather than the device handlers.  I know that the 
parallel port is on the first 8520 (CIAA), and that the register on this chip
dedicated to the parallel port is mapped in memory as a byte address at
BEE101. (page F-2 of the A/W hardware manual).

I am pretty sure (but not %100, hence the questions) I can send a byte to 
this location by;

	char *parpt;
	parpt = (char *)0xBEE101;   /* set up a pointer to the || port */
	*parpt = 0xFF;		    /* poke 0xff to the || port */

What I'm not certain about is making sure the 8520 will 1. accept this value
cause the || register was not selected first, and 2. is the register seletced
because the address BEE101 forces some address lines that are tied to the 
8520 logic to select the || port register?

I have been able to read from this address with no problem.  However, when
I write to and then read from it, it looks like the byte I sent it never got
there.  I have alreadyy set the data direction register on the 8520 pertianing
to PRB so that it can accept writes.  What am I missing?

Is the 8520 a cbm product, and is it documented anywhere?

I know that this is against all the rules for PUBLIC programming, i.e.
talking directly to the hardware.  But since I'm trying to access the || port
from CLIPS and LISP so that I can "talk" to my robot sitting on the || port, 
it wont bother anyone, unless of course, you would like to purchase my 
robot 8^).

Stergios Marinopoulos
S&M Engineering
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