Xref: news2.mv.net comp.os.msdos.djgpp:2453
From: mchyzer AT red DOT seas DOT upenn DOT edu (Michael C Hyzer)
Newsgroups: comp.os.msdos.djgpp
Subject: Accessing a Memory Location
Date: 4 Apr 1996 08:24:18 GMT
Organization: University of Pennsylvania
Lines: 35
Message-ID: <4k00vi$dqb@netnews.upenn.edu>
NNTP-Posting-Host: red.seas.upenn.edu
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

Hello,
I am running the same gcc for DOS on my pentium desktop and 386 laptop.  
I am trying to write to the address of the parallel port (0x0378 on both 
machines).  When i do it on the desktop, with a command such as:

int *para = (char *)0x0378;

This line causes a segmentation violation on the laptop.  When I use this 
line on the desktop, it will complete the assignment, and I can read and  
write to the address.  When I boot the desktop without drivers (hitting 
F5 during startup), the C program will not run, and the segmentation 
violation is identical to the laptop.  Another piece of information that 
might help, is that the memory addresses for normal assignments on the 
laptop consists of addresses such as: 0x7FFFFE58.  This is the same 
magnitude of address that the desktop uses when it does not run 
properly.  When the desktop does run properly, it uses addresses such as 
0x51E54.  It seems that when C uses this block of memory, it can access 
the memory address 0x0378.  But when C is using the high memory, it 
cannot access the low memory, even to read it.  

My question is:  Does anyone know how to load gcc so it uses low memory.  
I am using the same memory manager on both machines, and trying to  
duplicate the config.sys, but no luck.  
Does anyone know how to write to an address that is locked out by C using
usual commands.
Is there another easy way to change the pins of the parallel port without 
using C, if using C is unfeasable.  I want to change the voltage at 
certain pins without start and stop bits, or however it normally 
operates.   
If you dont have enough information, or you have suggestions, please 
email me at:
mchyzer AT seas DOT upenn DOT edu
Thank you very much.
Chris Hyzer