Craig:
I cannot tell exactly how much data that you are getting in each string from the serial port. I can see however that you are placing that data into an internal memory buffer beginning at address 0x20. (I suspect that the total data length is over 16 bytes of ASCII data). I can also see that inside the TD: time delay subroutine that you are using two memory locations 0x30 and 0x31 as counters in the delay routine. From my assumption above I suspect that the input ASCII data string extended from 0x20 to a bit past 0x31. It must be that the 0x30 and 0x31 locations are the same memory locations where the two latitude digits were stored. The TD routine leaves these at a value of 0x00 and later when you come to display the data taken from 0x30 and 0x31 you are sending these zero values to the VFD. The VFD probably displays the zero values as spaces.
Michael Karas