Nmea 0183 Format Control Messages; Beacon Monitor Control Messages; Section 10 - Nmea Protocols - NorthStar 8700 Technical Reference Manual

Section 10 - NMEA protocols

10.1 Beacon monitor control messages

10.1.1 NMEA 0183
format control
messages
05/01/97 REV H
This section supplies information for special applications and for when
you require manual control of the Northstar DGPS beacon receiver.
Messages to control operation of the Northstar DGPS beacon receivers are
accepted on either the monitor or control input ports, or both. Two con-
trol protocols are implemented: NMEA 0183 and binary; either or both
may be used. This section covers the NMEA 0183 format control mes-
sages, and Section 11 covers the beacon binary protocol.
These control messages are formatted according to a widely used NMEA
0183 specification, with serial communication parameters of eight bits,
no parity, and either a standard baud rate of 4800 or a nonstandard 9600.
NMEA messages begin with a $ character. They contain identification
and parameter fields separated by commas. They may also contain an
optional checksum (a hexadecimal value following an asterisk). If speci-
fied, the optional checksum is enforced, otherwise no checksum test is
applied. Normally, hard-wired serial data connections are so reliable that
the use of a NMEA 0183 checksum isn't required or recommended. The
messages end with a carriage return/line feed (CR) (LF) sequence.
NMEA 0183 format control messages are buffered within the beacon
receiver until the messages are ready to be processed, then they're ech-
oed back to the controlling device. Messages received on either the con-
trol input port or the monitor input port are echoed to the monitor
output port.
All alphabetical characters must be upper case, and messages must not
include embedded tab characters or spaces.
Here's the NMEA 0183 format basic tuning command:
$PSLIB,frequency(CR)(LF)
where frequency is a decimal value (in kHz) that specifies the radio-bea-
con frequency to be received and demodulated. This frequency can be
specified with up to four digits following the decimal point, giving a tun-
ing resolution of <2 Hz. This command tunes channel 1 of the beacon
receiver to the specified frequency, and presents its demodulated RTCM
SC-104 data to the GPS receiver; channel 2 continues to scan the beacon
band.
If you specify a frequency of zero in the basic tuning command, the bea-
con receiver is commanded back to its automatic mode:
When the bitrate of a broadcast is known as well as its frequency, it's
highly advantageous to specify it in an extended format tuning command
as follows:
$PSLIB,frequency,bitrate(CR)(LF)
where frequency is in the format specified above, and bitrate is one
of the values 0, 25, 50, 100, or 200. (The value of zero indicates that the
$PSLIB,0(CR)(LF)
Section 10 - NMEA protocols
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