The following list of bugs,  clarifications,  software routines to do certain interface tasks, and other information is compiled from user input.  YOUR input is invited.
Thanks
Joe Mehaffey

The following program will compute checksum required for each ASCII string sent or received from a Magellan GPS. The spec incorrectly states that the leading "$" and the trailing "*" should be included in the XOR computation of the checksum. NMEA specifications state that "$" and "*" should be excluded! My program takes account of this discrepancy.

Another important fact not stated in the spec is that the flow control in the PC should be set to NONE, otherwise data transfer is not possible. I found a good source for a Magellan interface cable with voltage regulator but no DB-9 plug for $19.95 +$6 S/H at: http://globe-mart.com/gps/magellan/accessories/gps315-gps320/730276.htm

10 PRINT  "Program to compute checksum by Cass R. Lewart 14 Sept 1999 "
20 LINE INPUT "Enter string to compute chksum, e.g., $PMGNCMD,VERSION* ",A$
30 L1=LEN(A$)
50 C=0
60 FOR I=2 TO L1-1
70 C=C XOR ASC(MID$(A$,I,1))
80 NEXT
90 B$=HEX$(C)
95 IF LEN(B$)=1 THEN LET B$="0"+B$
97 PRINT
100 PRINT "chksum of ";A$;" is - ", B$