Ruben Jvnsson wrote:
>
> > >Does anyone know off-hand the memory address and value for setting the
 RS232
> > >TX line high on a PC? I need to trigger a relay connected to this line.
> The baseaddress can be found in the ROM BIOS parameter area at
> addresses:
>
> 0000:0400 COM1
> 0000:0402 COM2
> 0000:0404 COM3
> 0000:0406 COM4
> 0000:0408 LPT1
> 0000:040A LPT2
> 0000:040C LPT3
> 0000:040E LPT4
>
> The ones that doesn't exist have 0 as baseaddress.

But beware!  Ports that are 'virtualized' under NetWare DOS clients have
"NW"
as their address value.  This is done so that programs that test just
for
presence of the port by looking for zeros find a port there (and writing
to
the port by means of the BIOS then will work because the NW client traps
that).  Because no parallel/serial port is present at that address,
you'd
better check for 0 as well as "NW" (0x4e57 or was it 0x574e?) there.

Frank
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Frank A. Vorstenbosch     <UCE_ACCEPT="NONE">     Phone: 0181 - 636 3000
Electronics and Software Engineer                 Mobile: 0976 - 430 569
Eidos Technologies Ltd., Wimbledon, London        Email: fav@eidos.co.uk