Now I'm moving on to my real radio, an Icom IC-T90A.  I found the following info:

But it has not produced fruit with the Icom CS-T90A software.  Specifically, it errors "Cannot access COM port."  If I remove the cable / diode from the header and jump TX and RX pins together, the CS-T90A software responds differently, indicating "No answer from the transceiver."  So, I know the software and the CP-2102 are talking.  There's a note in the instructions above about connecting the CTS and RTS pins together... which I can't do on the 2102 board I have.  The pins are on the IC of course, but not connected to anything on the board.  The diode I used appears to be good and electrically, the cable seems sound.  Any ideas?

BTW, I found a treasure trove of info on T90A programming, courtesy of Eric Behr at NIU.  I plan do dig into the following when I have a little more time:

http://www.math.niu.edu/~behr/Ham/Files/ic90memory.pdf

I would love to be able to easily port all the frequencies between my rig and my sons' rigs.

Chris, W1CAS