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RS232OFF.DOC
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1989-02-11
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35 lines
From: Dave Hershberger.
I have noticed and found a fix for a problem which occurs when
you use PROCOMM on COM3 and/or COM4. COM3 and COM4, when used
with PROCOMM 2.4.2, share the same interrups as COM1 and COM2.
That is, COM1 and COM3 share interrupt IRQ4 while COM2 and COM4
share IRQ3. This is fine as long as all programs which use the
COM ports tell the UART to "shut up" and get off the interrupt
bus before the programs terminate. Otherwise, bus contention may
occur. Two UARTs can both be tri-stated "on" trying to drive the
same interrupt. I have had the problem using PROCOMM on COM3 and
a Logitech mouse on COM1 with Generic Cadd. After using COM3 with
PROCOMM, for instance, then sometimes I could not run Generic
Cadd using the mouse on COM1. It was as though COM1 was not there
anymore. Similarly, sometimes after using Generic Cadd using the
mouse on COM1, COM3 did not seem to be there using PROCOMM.
CNTRL-ALT-DEL is not sufficient to clear the problem. The only
way to clear the bus contention was to turn the power off! After
conferring with a friend (Jim Michener, who gets credit for
writing the "RS232OFF" program), a solution was found. The
RS232OFF program simply sends a "shut up" command to all four
UARTs. The simple ten-line "c" source code as well as the
compiled .EXE files are included. If you have programs which
alternately use COM1/COM3 or COM2/COM3, just run RS232OFF between
them.
Date: February 11, 1989
From: Keith Petersen, W8SDZ
I rewrote the program in assembler to reduce its size.
Use shareware A86 assembler or debug to reproduce the
COM file.