Hi Ken,
According to page 19 of the Standard Horizon CP 175C manual, you can interconnect two types of GPS. They are referred to as GPS and Smart GPS. The GPS connections look to be NMEA, but unfortunately the instructions simply give directions as to how to interconnect different devices. They don’t give general information on the NMEA port settings. One could infer that their description of GPS antenna input (yellow wire) and GPS antenna output (pink wire) are simply GPS NMEA Rx and GPS NMEA Tx, but I am unsure. In any event, it’s probably worth it to get a NMEA GPS and have the output of the GPS go to both the CP 175C and your navigation laptop. If it was my own boat, for simplicity, I’d suggest going with the Standard Horizon GPS option.