COMOFF Version 0.3 - Takes All UARTs Off The Interrupt Bus (For IBM-Compatibles)
(Inspired by the DOS freeware source code RS232OFF.C by Jim Michener)
Freeware from Kirk Lawrence


THE TECHNICAL BACKGROUND:
When more than two COM ports (COM1 and COM2) are installed in an IBM-
compatible computer, the conventional configuration is to have COM1 and
COM3 share IRQ4, and to have COM2 and COM4 share IRQ 3.

However, only ONE device can actually USE any IRQ at any given time.
This means that if you have a serial communications device (such as a
mouse) installed on COM1, then there should be no serial communications
device (such as a modem) in use on COM3.  Since COM1 and COM3 share a
common IRQ, attempting to use two serial devices on the same IRQ will
cause conflicts, and one or both of the devices will not operate properly.
The same is true if serial communications devices are installed on both
COM2 and COM4.

THE PROBLEM:
Occasionally, it may be necessary (for whatever reason) to install serial
communications devices on COM port numbers which share a common IRQ.  Also,
on occasion, the very presence of an installed (though unused) COM port
may, itself, conflict with an installed serial device sharing the same IRQ.

THE POSSIBLE SOLUTION:
It's sometimes possible to resolve such IRQ conflicts by putting the of-
fending port(s) "to sleep."  This is what COMOFF does.  COMOFF tells all
the UARTs in the system to "shut up" and get off the interrupt bus.  Doing
this will SOMETIMES allow the use of a serial device on a COM port which
is sharing its IRQ with a serial device on another COM port.  The operative
word here is "SOMETIMES."

TO USE THE PROGRAM:
At the CP/M-86 command prompt, type COMOFF  ...and then press the ENTER key.

NOTE WELL: You must run COMOFF each time you change active devices which
are sharing a common IRQ.  Accessing a COM port with interrupt-driven soft-
ware places the UART chip back ON the interrupt bus.

Please understand that using COMOFF does NOT "disable" or "remove" the COM
ports.  The ports are still "there," and can be accessed by any interrupt-
driven software, such as a modem communications program.  COMOFF only takes
the COM ports' UARTs off the interrupt bus temporarily...which will sometimes
resolve IRQ conflicts.

COMOFF is not magic, and it won't solve all IRQ conflict problems.  Use
common sense in your assignment of serial communications devices to COM
port numbers.

COMOFF.CMD is free.  As is always the case with "freeware," there are NO
guarantees whatsoever.  If you use the program, you do so entirely at your
own risk and peril.  Your use of COMOFF.CMD shall be prima facie evidence
under law the you understand and accept these terms and conditions.