| COM port address/irq DEBUG
A simple way to detect problems w/COM ports is to go to a DOS command
line nearest your present environment (real DOS, DOS under OS/2, or DOS
under Windows).
Enter DEBUG at that DOS prompt. Enter D 40:0 at the "-" (dash)
prompt. To exit, enter Q at the "-" (dash) prompt.
On an ISA system, 4 COM ports would look like the following. If
you have fewer ports, their base I/O address will be 0000 instead of what
is shown.
0040:0000 F8 03 F8 02 E8 03 E8 02-xx xx xx xx xx xx xx xx
COM1
COM2 COM3 COM4 LPT1 LPT2 LPT3
3F8
2F8 3E8 2E8
On an MCA system, 4 COM ports would look like the following. If
you have fewer ports, their base I/O address will be 0000 instead of what
is shown. The COM and LPT port positions are shown below the example
dump.
0040:0000 F8 03 F8 02 20 32 28 32-xx xx xx xx xx xx xx xx
COM1 COM2
COM3 COM4 LPT1 LPT2 LPT3
3F8
2F8 3220 3228
If your dump doesn't look like this (except for 0000 in known to be
nonexistant port positions *only* after the last known existing port),
then you must make a configuration correction in order for any port, not
just an Mwave port, to work reliably under all environments.
Regarding IRQs, IRQ 4 and 3 can be shared but it is just a bit different
for ISA verses MCA.
ISA MCA
COM1
4 4
COM2
3 3
COM3
4 3
COM4
3 3
Once you start using COM3 and COM4, you will find that you may have
to tell your COM driver and your software explicity what base I/O address
and IRQ those are. OS/2 will require one of the following added to
the COM.SYS line (or equivalent) in CONFIG.SYS (shown as "ISA or MCA").
(3,3F8,4) (4,3F8,3) or
(3,3220,3) (4,3228,3)
OS/2 WARP Bonus Pack Faxworks requires the same thing as COM.SYS does.
On ThinkPads, this is true even if your port is COM2, for example.
So, (2,2F8,3) must be added to the FMD.SYS line in CONFIG.SYS.
It has also been seen that ThinkPads either do not have COM.SYS and
VCOM.SYS in their CONFIG.SYS or their DEVICE statement points to the THINKPAD
directory instead of the OS2/BOOT directory. In either case, the
Mwave port just seems to mysteriously not work.
It has been suggested that using (n,aaa,i,,F) instead of (n,aaa,i) will
insure that the COM dirver is aware of the Mwave port's FIFO on ThinkPads.
I have not found documentation that supports this.
Serial mouse drivers seem to be sensitive to sharing IRQs on ISA systems.
So, for example, this would need to be the configuration...
Serial modem in serial port A as COM1 as IRQ 4
Serial mouse in serial port B as COM2 as IRQ 3
MWAVE modem
as COM3 as IRQ 4
Instead of...
Serial mouse in serial port A as COM1 as IRQ 4
Serial modem in serial port B as COM2 as IRQ 3
MWAVE modem
as COM3 as IRQ 4 |
