Any suggestions for a "dual port" version of PortMon that could monitor traffic between two serial devices? LIke, say, a head unit and a tuner box?

You'd need to connect the TD line from each device to an RD line on a serial port, but that's doable.

I guess I could write something that "shorted" the serial ports together, and then just run PortMon on one of them. That probably wouldn't introduce enough delay to matter.

-Z

PS: Linux solutions would work, too.