Humminbird Matrix Series: searching for schematic pinout t..

HI,

I'd like to make my own cable to connect my fishfinder HUMMINBIRD
Matrix 15 to PC Serial Port (rs232).

I've found the cable ready-made but it's too expensive. I thinks the
price is very high for 2 plastic connectors (Serial 9 Pin for PC RS232
and another plastic connector) for the fishfinder, connected together
with a simple electrical cable.

Is there anyone who's got the schematic or pinout (pinouts) of the PC
LINK CABLE (to connect humminbind matrix fishfinder to PC)?

Thanks a lot for your answer.

llull