how do I tell if my sio0 port is broken?

[Zhang Weiwu]

Hello List. I guess my sio0 port is broken on my Thinkpad, OS is
FreeBSD-6.1. Reason:

1) I have tested a null-modem serial cable is working by using it on a
dumb-terminal and a headless server. With the same cable and same
headless server, but replace dumb-terminal with my thinkpad, run

$ tip com1
connected

Then, whatever key I press, nothing happens. Usually I should see login
prompt after I pressed "Enter" key. Test was done with FreeBSD Generic
kernel.

2) I have plugged a modem (with ordinary serial cable, not the
null-modem one) on it and run minicom. If I type 'at' I should get 'OK'
as prompt, but I didn't. The same modem and same cable work for another
Linux box.

3) I go to BIOS and do a serial port test, test result is "OK", but I
think bios have no knowledge if a port is broken when it's not connected
to anything at all.

So, I think next morning I should go and check if there are PCMCIA card
that can provide an extra COM port, but before that I think I should
write this letter to the list to see what you guys would do in this
case: do you also think this looks like COM1 port is broken?

Thank you very much for advices.

Zhang Weiwu