On 31 Jan 99, at 23:58, Kenneth Alan Boyd Ramsay wrote:

> Something I have used to figure out older (ISA) motherboard/video
> problems: I used an old MDA (Monochrome Display Adaptor) video card and
> monitor. Using DOS, and the MODE MONO command got the MDA monitor working.
>  Using the MODE CO80 (cee-oh-eight-zero) with BOTH cards plugged in
> allowed me to switch to a VGA monitor.
>
> This allowed me to see what I was doing using the MDA monitor and then
> switch to the VGA monitor to see the results.  I could try different
> drivers, etc.; and if something didn't work, I could switch back to MDA
> and try again.

  Note that this was possible because the MDA and the CGA (which the VGA
was emulating in this case) used different device I/O addresses and
different memory buffer addresses.  The MODE command swapped which set
of addresses the BIOS-level display output routines would use.

  This was a preferred debugging environment for Win 3.x, with Windows
running on the VGA monitor and the CodeView debugger on the monochrome.
We called such a machine a "two-headed monster".

> I understand that there is a potential for damaging a monitor by
> setting too high a horizontal frequency for a particular monitor, but
> with a little care (and perhaps a little luck :-), it worked for me.

  MDA and CGA map similar functions to distinct rages of I/O addresses.
There were some values that were valid for CGA but deadly to MDA monitors,
but you'd have to be writing such a value to the wrong address [whether
carelesly or maliciously] to ever cause damage.

> Does anyone know if this could be adapted to the Gateway and monitor in
> question?

  Unless he's got a spare TTL monitor around for the MDA, I don't see
how this helps.


David G

                         PCBUILD's List Owner's:
                      Bob Wright<[log in to unmask]>
                        Drew Dunn<[log in to unmask]>