[Xastir] serial comms lost... I can't figure this one out.

[mark]

I can't figure this one out...  Somehow I've lost serial communications
between Xastir and the serial TNC.  I'm at the end of my rope...

With Xastir killed, I can bring up picocom using the command line:

   picocom -d 9600 -p even -d 7 /dev/ttyS0

And I can see TNC traffic streaming out of my TNC... no problem:

   KC5EZZ-10>W5EEY-3*>WIDE5-2>APRS:!3117.23NN09951.27W#PHG7440 
   KC5EZZ Digi Eden, Texas

So, I kill picocom, and start Xastir.  The serial settings in Xastir
match those above for the Serial TNC (not the Serial KISS TNC).  I've
checked everything I can think of...     

Under the menu Interface>Interface Control, if I highlight 
    "Device 0  DOWN  Serial  TNC  /dev/ttyS0" 
and click on the "Start" button, the highlighting goes away, but the
interface is still shown as "DOWN".  The startup file that I've created
(and have had working for days...) exists and is called out in the TNC
Config Menu correctly (I've checked the file name twice).

This setup USED to work... but somehow I'm overlooking something real
basic...

Under the menu View > Incoming Data, I have "TNC Data only" selected,
but there's no incoming data to view... because the interface is thought
to be "DOWN" still.  I can kill Xastir and bring up picocom again, and
the serial stream of traffic continues to flow out of the TNC. I just
can't see it in Xastir.

I've also tried deleting the Device 0 in Xastir's Interface Control and
rebuilding the configuration, but I still can't get anything going.

I've also cycled power on the TNC... but that's not changed a thing...

Now, what the heck am I doing wrong?  I'm really stumped.

OS: Fedora Core 5
Xastir: 1.8.4
TNC: Heathkit HK232

- Mark 
N4CMB