Hi Deniska.
I gave up trying to get the Garmin GPSIII to work with Mapthis. So I just recently bought a Holux GR-231 secondhand. After a bit of stuffing around, finally got it to work fine with the program. To get it to work, I have not used any resistor. This is important.
Also, when I first started the program, & the GPS was locked on, Mapthis at first said "Bad Data".
I then opened the GPS Test program to verify the data was ok, & it was. The went back to Mapthis, & behold, the data was OK ! It's as if the serial port needed initialising or something with the Test program first. GPS comms are working fine every time now.
I am using the default Readtime of 1.
Really look forward to driving around with the PSP now ! This is a great program.
Cheers, Chris.