Garmin GPS 16-HVS Руководство по эксплуатации - Страница 14
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Appendix A. CR23X/CR10X Programs
A.1 Programming
A.1.1 Program Execution Interval
A.1.2 Reading GPS Data
Program instruction 15 (P15) is used to read the NEMA $GPGGA string of
time and position data. Each iteration of P15 can either read the numeric fields
or read everything. When reading the numeric fields, such as time, latitude,
longitude and elevation, P15 requires non-numeric delimiters between data
points. The only available format of GPS data with delimiters is the NMEA
0183 format. Program instruction 15 (P15) reads serial data and discards non-
numeric values. All non-numeric values act as delimiters between numbers,
and decimal points can also act as delimiters. P15 can be used to import
everything in the string, character by character, and convert it to the decimal
equivalent. The decimal equivalent method is seldom used, and only when the
general area (hemisphere) is not known.
Due to the sequential program instruction execution of the CR10X and CR23X
the Port Interrupt Subroutine 98 is useful in synchronizing the GPS16-HVS
measurement via the Pulse Per Second output. When the PPS signal is used to
trigger the read data function (P15), the program table execution interval does
not matter. Otherwise the timing between the GPS16-HVS output and the
datalogger read must be considered. Generally the execution interval can not
be less than 2 seconds when the PPS signal is not used. This is discussed
further in Section A.1.5.
Table A-1 is a sample CR23X P15 instruction for reading NMEA $GPGGA
data string. The second parameter has two dashes indicating data buffering has
been turned off. The CR10X does not have the data buffering option.
TABLE A-1. P15 for NEMA $GPGGA Data String
Parameter
Data
Description
1
1
Repetitions
2
61 --
Configuration code for RS232 ASCII data at 1200 baud
with data buffering turned off. The -- indicates data
buffering turned off. Decimal delimiter
3
1
Delay before sending data out
4
05
Control ports. Two digit format AB. A is for
handshaking and set to zero. B in this example is control
port 5 (datalogger RCV). GPS16-HVS communication
cable: GPS transmit to control port 5 in this example
5
1
Input location where first character to transmit is stored.
Note: nothing is actually transmitted
6
0
Number of consecutive input locations to send
7
42
Termination character, 42 is ASCII equivalent of the
asterisk
8
100
Maximum number of characters to receive.
9
80
Delay in mS. How long to wait for $GPGGA string
10
1
Starting input location for time and position data
A-1