Few time ago, I read some requirement for help in order to interface
a YEASU CAT SYSTEM to a Computer. 
Hereafter, what I'have done to drive a FT-767 with the RS232C of a
computer.

 DB25S (Computer side)                         DIN6 (TRCVR side)

                             | /-----------------       3 SI
  2 TD      -----/////-------|<
                  10K        | \   NPN 2N2484
                                V   ou equi.
                                |
                              __|__

  7 GND     -------------------------------------       1 GND

                             
  3 RD      ----------------\ |
                  |          >|------//////------       2 SO
  4 RTS  _        |         / |       10K
  5 CTS  _|       |        V
                  |        |    NPN 2N2484
                  /      __|__   ou equi.
                  /
                  / 10K
                  /
  6 DSR _         |
  8 CD  _|________|
 20 DTR _|


This is wired directly on the DB25S connector and is fitted in the
cover after some drops of epoxy.
The next step is, using your favorite compiler, to write down a program
to suit your needs.
Remember to switch on the CAT first, and to switch it off at the end of
your instructions, if you have to operate manualy the rig later on.