Garmin GPS 16-HVS Instruction Manual - Page 14

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1. Wiring

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

Repetitions

61 --

Configuration code for RS232 ASCII data at 1200 baud

with data buffering turned off. The -- indicates data

buffering turned off. Decimal delimiter

Delay before sending data out

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

Input location where first character to transmit is stored.

Note: nothing is actually transmitted

Number of consecutive input locations to send

Termination character, 42 is ASCII equivalent of the

asterisk

100

Maximum number of characters to receive.

Delay in mS. How long to wait for $GPGGA string

Starting input location for time and position data

A-1