Appendix A. CR23X/CR10X Programs
GPS fix. A better approach is to overwrite the GPS quality location with zero
before executing P15. Use P30 to overwrite one input location.
If the GPS time is used to set the datalogger clock, the GPS time must be
parsed into three input locations: Hour, Minutes, Seconds. P114 is used to set
the datalogger clock to match values in input locations. Some time will have
passed between the GPS fix and when the program table reaches the P114
instruction. Adjustments can be made by adding a second or two. Be careful
about setting seconds to a number greater than 59. You can also correct the
UTC time to local time. Table based dataloggers require year, day, hour,
minute, and seconds to use P114. Only hour, minutes, and seconds are
available from the $GPGGA string. The PGRFM string includes the month,
day and year, but is difficult to use.
A.1.5 Program Discussion
Wiring when using RJ45 adapter:
Function Color
Datalogger
Connection
Power in
Blue
12 volts
Power ground
Orange
Ground
Power switch
Black
ground
TXD Green
C5
PPS Yellow
C8
The Garmin16-HVS should be setup for 1200 baud, 8 data bits, 1 stop bit and
no parity. The GPGGA string should be output. The 1 pulse per second signal
should be output with a pulse duration of 80 milliseconds.
The code required to read the GPS information and store it to final storage is in
Subroutine 98. Subroutine 98 is interrupt driven and triggered when a rising
edge is detected on Control port 8. The Garmin16-HVS has a 1 PPS signal
which is wired to control port 8. The transmit data line of serial port 1 on the
Garmin16-HVS is wired to control port 5. The Garmin16-HVS serial port 2
generally is not used.
When the 1 PPS signal triggers subroutine 98, P15 is executed. P15 is setup to
read ASCII serial data. Each data point is separated by a non-numeric
character or a decimal point. Fifteen input locations are used as temporary
storage for the $GPGGA string. Table 3.1 explains the $GPGGA string.
The input locations used for the $GPGGA string are:
1) Raw_Time, Time in hours, minutes, and seconds
2) LatDegMin, Latitude degrees and minutes
3) Lat_Frac, Latitude fractions of minute
4) LngDegMin, Longitude degrees and minutes
5) Lng_Frac, Longitude fractions of minute
6) Quality, GPS quality indicator
7) NumSats, Number of satellites in use
8) HDPWhole, Horizontal Dilution of Precision
9) HDPFrac, Horizontal Dilution of Precision, tenths
10) Elevation, Elevation in meters
11) Geoidal, Geoidal separation in meters
12) Geoidalth, Geoidal separation in meters, tenths
13) Age, Age of differential GPS data
14) Agetenth, Age of differential GPS data, tenths
15) DiffID, Differential reference station ID
A-4
