Dec 142017
Set COM3 and COM4 in Windows 3.0. Includes ASM source code.
File SETCOM.ZIP from The Programmer’s Corner in
Category Windows 3.X Files
Set COM3 and COM4 in Windows 3.0. Includes ASM source code.
File Name File Size Zip Size Zip Type
COMHELP.TXT 1327 748 deflated
SETCOM.ASM 232 133 deflated
SETCOM.COM 25 25 stored
STDMAC.INC 2992 1064 deflated

Download File SETCOM.ZIP Here

Contents of the COMHELP.TXT file

Here's some help. I just spent a week figuring this one out. If you're using
DOS 4.01 (probably some others too), it already knows about COM3 &4. Most
BIOS's only scan for COM1 &2 though. You can test this by trying to open COM3
at the DOS prompt--if you get 'illegal device' then fix will work. The ROM
BIOS checks for comm ports and if found puts their I/O addresses at absolute
memory location 0x400 (400h, or 40:0). If you set locations 0x404 & 0x406 to
the I/O addresses of your COM3 & 4 port (normally 0x3E8 & 0x2E8) then try to
open the COM port as a file to see if that fixes it. By 'open file' I mean try
'copy x com3' where x is a small text file. After the fix you may not get
'illegal device' but another error message caused by the retry default of the
com port--this is not a problem for windows though.

What I did was to write a tiny assembly language program to stuff these values
into low memory during the Autoexec. I you like I could upload it.

I also found that programs other than terminal which directly access the comm
ports (e.g. ProComm) worked, but dropped characters in doing downloads in the
background at 2400 BAUD. Once COM3 &4 were logged in, apparently windows does
some buffering of its own.

Good luck,
Rod Allen

 December 14, 2017  Add comments

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