GPS16X-HVS GPS Receiver
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End Program
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A.1.6 Troubleshooting
The first step is to verify that it really does not work. With the GPS16X-HVS
running and the datalogger program running, look at the input location for GPS
Quality Number. This location will show a one when the GPS16X-HVS output
is picked up by the datalogger. The input location for parsed time and position
are good locations to check. The location for seconds should update every time
the GPS data is updated.
If the GPS time and position data are not shown in the input locations, check
the communication cable wiring.
If the GPS16X-HVS data is not correct every program table execution but
correct sometimes, check the P15 time-out. It may need a longer time-out.
Also check the P15 maximum number of characters to receive, usually 100 is
enough. Check the P15 termination character; it should be set to 42 (*). The
termination character should also work if set to 13 or 10. Also check the
buffering and filter. Buffering should be turned off. On a CR23X, index
parameter 2.
For P15 to properly read the $GPGGA string, P15 must be executing while the
$GPGGA string starts and finishes. The P15 time-out needs to be long enough
to pick up the string. The string is output once a second. If P15 starts to
execute while the GPS16X-HVS is sending the string, P15 must wait until the
string is sent again plus the amount of time it takes to send the string. It
shouldn’t need more than 1.5 seconds. P15 time-out is in units of 0.01 seconds,
100 = 1 second. A longer time-out will force the datalogger to wait until the
time-out has expired or the termination character is received or the maximum
number of characters are received. If the data in input locations 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 (CR23X only) 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.
(78 paginas)
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