From:	kunst AT prl DOT philips DOT nl
Subject:	Re: Text mode versus graphical mode.
To:	A DOT APPLEYARD AT fs2 DOT mt DOT umist DOT ac DOT uk (A.Appleyard)
Date:	Tue, 21 Mar 1995 13:08:20 +0100 (MET)
Cc:	djgpp AT sun DOT soe DOT clarkson DOT edu (DJGPP users list)

Anthony Appleyard writes:
> 
> According to a manual that came with my PC:-
> Addresses 0xb0000000 etseq are the screen when in black & white text modes.
> Addresses 0xb8000000 etseq are the screen when in color text modes,
>                                   or in graphical modes 4,5,6.
> Addresses 0xa0000000 etseq are the screen when in graphical modes >= 0xd.
>   (But otherwise when in Gnu C).
>   Is this still all always correct?
>   I wrote a program (a text editor called AAEMACS) that needs the PC's screen
> to be in a text mode. It tests for mode type thus:-
> 
> #define uns unsigned
> uns char*graphicalscreen=(uns char*)0xd0000000; /**** this addr only in Gnu C */
> 
> and I set the byte graphicalscreen[44] = 16. If thereupon the byte
> graphicalscreen[44] == 16, then the graphical screen address range exists and
> I am in a graphical mode, not a text mode, so I complain and exit. This has
> always worked OK so far with me, lots and lots of times. But a few days ago I
> put AAEMACS on Simtel, and I got today an email from someone saying this:-
> 
> > I just downloaded Aaemacs from SimTel. I set the environment variable
> > AAEMACS, but when I tried
> >     aaemacs readme
> >   I was told that aaemacs could not go into my screen mode-- 3 as reported
> > by FINDMODE. It is the standard 80x25 with brightwhite text on a blue
> > background. Any help would be appreciated.
> 
>   (1) Are there any PC's or PC screen chips where the graphical screen range
> 0xa0000000 etseq always exists even in text mode?
>   (2) He said that his mode 3 displays bright white on blue, not ordinary
> white on black, as if something has reset it. Are there any packages or
> programs etc that when loaded or set by CONFIG.SYS or AUTOEXEC.BAT, will set
> up a condition whereby the graphical screen address range always exists even
> when the screen is in text mode? I compiled the corrent version of AAEMACS
> with my current version of djgpp, which is go32 1.12, binutils 2.4, bison
> 1.22, diffutils 2.6, flex 2.4.7, gas 2.3, gcc 2.6.0, gdb 4.12, gzip 1.2.4,
> libg++-2.6.0, make-3.71, patch-2.1, sed-1.18, texinfo-3.10 .
> 

You can never access the screen directly via 0xa0000000 with DJGPP !

Note: 0xb8000000 should be read: b800:0000 (seg:ofs), or: b8000 linear.
This location can be accessed directly via 0xe00b8000 etseq.

You can access DOS memory directly via 0xe0000000 but this is considered
obsolete (i.e. doesn't work with DPMI, and thus not in Windows DOS boxes
or V2). 

Use dosmemput() instead, or the far pointer routines <sys/farptr.h>.

Please make the change to dosmemput(), even if it is some work initially.

Pieter.

- Raw text -