Have no experience of this particular GPS, but if you can connect to a PC then the user hand book will tell you which pins from the connecting socket carry which info to the computer and from the computer if you are intending to use a chart plotter and download waypoints onto the GPS.
Have used a Garmin with dedicated lead which was brilliant and also a Philips which I had to make up the cable for but all info was in the user handbook.
Not sure if this will help. I have a GP31 and the manual says that "the power supply port is commonly used for connection of external equipemnt such as a PC" It then refers the reader to the wiring diagram which indicates that the yellow and green should be fitted to an RS232C (isn't that a serial port) connection. It says the yellow is 'SD' and the Green 'RD'.
I don't have a laptop or PC connected but have a variety of makes of kit and so have a little black box from Autohelm which takes all the different signals on my 'system' and makes them talk. I mention it because the black box has a terminal to wire in from a laptop - got it from Greenham Regis but it wasn't that cheap £90 I think but cheaper than getting an new Autopilot that talked the right language.
It is very easy - I did this on my model 31. There is a cable which comes out of the back of the unit which allows NMEA input as well as output - assuming the GP30 is similar to the GP31. Consult your manual for the actual wires to connect to a PC or laptop serial port. If you have a new laptop without serial port you will need to purchase a USB to Serial convertor - just a small cable with a bubble of electronics costing about £30 (Maplin). Remember you need to set up the input and output of the GPS to output the datastream you need. What are you going to do with the data though? I run my whole boat navigation via a chartplotting program (SeaPro) but there are other varieties of this kind of software too. I use the GPS input to upload waypoints from laptop to GPS for emergency use. Come to think of it, my unit has a setup screen giving a wiring diagram by selection via the menu system!!! If you need wire by wire details email me direct and I will get the info from my boat when next I am down.
I have this set up on my boat. The wiring diagram in the manual gives you the colours for the data-in, data out wires. As the others have said, you need an RS232 serial plug to connect to the laptop.
Take some time to be sure that you connect up the serial cable correctly. It is easy to get things wrong and you will be pulling your hair out trying to discover why it doesn't work.
I find the setup is excellent. The NMEA data stream gives me a feed into my autopilot, radar etc as well as the laptop, which stays below and has quite a long cable run. I can, but don't, have the autopilot steer to the next waypoint.
