Campbell GPS16X-HVS Manual de instrucciones descargar pdf (Pagina 15)

GPS16X-HVS GPS Receiver

Appendix A. CR23X Programs

A.1 Programming

Program instruction 15 (P15) is used to read the NMEA $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.

A.1.1 Program Execution Interval

Due to the sequential program instruction execution of the CR23X the Port

Interrupt Subroutine 98 is useful in synchronizing the GPS16X-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 GPS16X-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.

A.1.2 Reading GPS Data

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.

TABLE A-1. P15 for NMEA $GPGGA Data String

Parameter

Data

Description

Repetitions

63 --

Configuration code for RS232 ASCII data at 4800 baud

with data buffe

ring 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).

GPS16X-HVS

communication

cable: GPS transmit to control port 5 in this example

Input location where first character to transmit is stored.

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 29 30

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