Path: utzoo!attcan!uunet!know!zaphod.mps.ohio-state.edu!swrinde!emory!mephisto!prism!bb16
From: bb16@prism.gatech.EDU (Scott Bostater)
Newsgroups: comp.lang.pascal
Subject: I/O Port weirdness
Message-ID: <14401@hydra.gatech.EDU>
Date: 2 Oct 90 14:39:28 GMT
Organization: Georgia Institute of Technology
Lines: 44

This sort of half belongs in this newsgroup and half in c.s.i.p.hardware, but
I didn't want to take the flak for using Pascal instead of C :-)

I've run into a problem/bug with TP IDE and the use of I/O ports.  I'm trying
to read from an I/O port. Sometimes it works, sometimes it doesn't. 

Program Test;

var
  a: Byte;

Begin
  a := Port[$300];
  Writeln( 'a = ', a);
End.

This simple program has several different outcomes depending on the machine
I run it on and whether I use the IDE or use the command line compiler.  The
program behaves properly when compiled with TPC and executed via TD.

Machine                IDE         Result
--------              ------       ----------------------
IBM XT  (true blue)     Yes        Reboots Computer
IBM XT  (true Blue)     No         a = 175
80386 clone             Yes        a = 255
80386 clone             No         a = 255

During the testing process, I ended up pulling all of the "strange" cards out
of the XT so that now there is only a CGA card, Floppy controller, HD 
controller, and Multifunction I/O board (384K/1s/1p/1g).  

The port I'm trying to read from is $300, which does not exist in either 
machine.  I would expect to get $FF back from reading it (since the data lines
should float high).  

Has anybody else experienced this problem?  Anybody have an idea has to how to
fix it?  I'ld really like to be able to use the IDE because I'm used to it, but
I'd also like to know what's causing the problem.

-- 
Scott Bostater      Georgia Tech Research Institute - Radar Systems Analysis
"My soul finds rest in God alone; my salvation comes from Him"  -Ps 62.1
uucp:     ...!{allegra,amd,hplabs,ut-ngp}!gatech!prism!bb16
Internet: bb16@prism.gatech.edu