[comp.sys.ibm.pc] Intermittent problem with Serial Port on XT

albert@endor.harvard.edu (David Albert) (05/05/90)

I installed a new Multi-IO board on my XT recently, and ever since
have had problems with my (old) serial ports.  (I had trouble with
the serial ports on the new board, so I disabled them both.)  Here's
the problem:

About half of the time, when I turn on my computer, the COM1 port
hears the keyboard but does not respond to the monitor.  That is,
if I turn on my modem, connect and type "atdt" I see the lights flash
on the modem, the phone dials, and the lights flash some more when
the remote host presumably sends its login message, but none of the
text (including what I type) shows up on my screen.  The other half
of the time, the port works normally.

What might cause this problem?

Thanks,
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David Albert			| Fanatics may defend a point of view
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jbloom@uhasun.hartford.edu (Jon Bloom) (05/05/90)

In article <2785@husc6.harvard.edu>, albert@endor.harvard.edu (David Albert) writes:
> I installed a new Multi-IO board on my XT recently, and ever since
> have had problems with my (old) serial ports.  (I had trouble with
> the serial ports on the new board, so I disabled them both.)  Here's

Probably the new board is trying to use the same interrupts as the old
ports (IRQ3 and 4).  Or, even worse, the same addresses (but you say you
tried disabling them, so probably not addressing).  If the multi I/O
card has interrupt jumpers, try pulling them off altogether and see if
that lets the other ports work.