Campbell Scientific GPS16X-HVS GPS Receiver - Manual (Page 33)

Appendix B. CR23X Wiring and Programming
seem to move from the proper input location to another input location, P15 is
stopping before the entire string has been read. An example is latitude being
displayed in the time field, then in the latitude field. P15 works best when P15
quits reading data because the termination character has been read. Using the
PPS to trigger subroutine 98 is the best way to start P15 just before the
GPS16X-HVS sends the $GPGGA string. If the PPS signal pulls C8 high
while the datalogger is in the middle of executing an instruction, it may not be
able to run subroutine 98 before the $GPGGA string has started, which will
cause the datalogger to miss the data string. Turning on the data buffering may
remedy the problem. Lengthening the serial time-out to allow P15 to execute
for 2 cycles of NMEA output may help. Otherwise the SDM-SIO4 may be
required or the datalogger program will need to be simplified.
The datalogger will not pick up valid data until the GPS16X-HVS has a valid
GPS fix, except during a GPS16X-HVS warm start where time can be read
before position is known. Don’t spend a lot of time trouble shooting a
phantom problem just because the GPS receiver does not have a valid GPS fix.
B-9