COM4 AND COM3

 BBS: Inland Empire Archive
Date: 02-11-93 (09:21)             Number: 385
From: MICHAEL LOWE                 Refer#: NONE
  To: DIK COATES                    Recvd: NO  
Subj: COM4 AND COM3                  Conf: (2) Quik_Bas

I've been supporting Com ports 3 and 4 for some time now,
using the methods described in this thread, with very few
problems.

All you have to know is what IRQ is required (3 or 4) and
what base address (anything) to point to.

If you need IRQ 4, simply put the address into the COM1 pointer
for IRQ 3 use the COM2 pointer.

in decimal:
Seg  Offset
0000:1024 low byte com1
     1025 high byte com1
     1026 low byte com2
     1027 high byte com2

A few caveats...


It seems that after opening the port, QB zeroes out the
pointer.  If you need to use the address, don't count on
it's pointer being there while the port is open.

Recently, I've experienced problems with my terminal
program locking up after closing the port (If on com3 or 4)
IF and only if Telix v3.20 has been used during the current
boot.
I haven't a cluse as to why this is, but I believe it's
because of IRQ masks not being reset.. ..longshot..

                        Mike Lowe


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