NorthStar 8700, Technical Reference Manual

Page: 55 / 85

Section 10 - NMEA protocols
05/01/97 REV H PAGE 45
10.2 GPS serial protocol
This section describes the serial protocol used by the GPS sensor to com-
municate with the host device. The serial communication runs under the
following setup:
•
Speed: 300 to 38,400 baud (default is 4800)
•
Format: 8-bit data, 1 start bit, 1 stop bit, no parity (10 bits/character)
Data information passed on the serial line is divided in one or more
NMEA-approved or proprietary sentences having the following structure.
Table 21: Approved sentence structure
Table 22: NMEA field definitions
$PSLIB,0,(CR)(LF)
Return to automatic mode. The best broad-
cast available will be demodulated.
$PSLIB,,,R(CR)(LF)
Restart.
$PSLIB,284.5,0(CR)(LF)
Demodulate data from a DGPS beacon
broadcast at 284.5 kHz, with the bit rate to
be automatically determined.
Data field Contents
$PMCAG,xxx,xxx,xx,xx,...*CK<CR><LF>
$
Record sync character
P
Special ID (P = proprietary)
MCA
Originator ID (MCA = Canadian Marconi Company)
G
Interface ID (G = GPS)
xxx,xxx,x
x,xx...
Data (first field = message identifier)
*
Checksum field delimiter
CK
Checksum
<CR><LF>
End of sentence
Field type Symbol Description
Special format fields
Status
A
Single character field:
A = Yes, data valid, warning flag clear
V = No, data invalid, warning flag set