GPS module + PIC

[ScaleRobotics]

Here is one check sum solution for gps:

gpsdata         var byte[82]       ' Max length of a GPS sentence is 82 bytes.

DoCS:
    i = 0                             ' Initialize the position counter
                
    WHILE gpsdata[i] != "*"           ' Count everthing until the *
        cs = cs ^gpsdata[i]           ' XOR for checksum
        i = i + 1                     ' Increment position counter
    WEND

    ' A quick and easy atoh function
    ' Make it a seperate label if we add more atoh conversions in the future
    LOOKDOWN gpsdata[i+1],["0123456789ABCDEF"],tempbyte
    gpscs = tempbyte * 16        
    LOOKDOWN gpsdata[i+2],["0123456789ABCDEF"],tempbyte                
    gpscs = gpscs + tempbyte
        
    ' Flag bad data "V" if checksum doesn't add up. 
    ' Or if the sentence is less then 20 chars long
    ' Which means there is no active waypoint to go to.
    ' Should be "A" otherwise.
    IF (cs != gpscs) OR (i < 20 )THEN 
          gpsvalid = 0
    ELSE 
          gpsvalid = 1
    ENDIF   
RETURN