User Manual Part 7

User Guide to Q4000/QPRO
Document Number 1135-4713 Rev G
THIS DOCUMENT CONTAINS CONFIDENTIAL AND PROPRIETARY INFORMATION OF QUAKE GLOBAL CORPORATION. IT MAY BE USED BY
RECIPIENT ONLY FOR THE PURPOSE FOR WHICH IT WAS TRANSMITTED AND WILL BE RETURNED UPON REQUEST OR WHEN NO LONGER NEEDED
BY RECIPIENT. DISCLOSURE TO UNAUTHORIZED THIRD PARTIES OR DUPLICATION WITHOUT THE EXPRESS WRITTEN PERMISSION OF QUAKE
GLOBAL IS PROHIBITED.
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NMEA has the following application layer protocol rules:
• Each message's starting character is a dollar sign. 
• The next five characters identify the talker (two characters) and the type of message
(three characters).
• All data fields that follow are comma-delimited.
• Where data are unavailable, the corresponding field contains NULL bytes (e.g., in
"123,,456", the second field's data are unavailable).
• The first character that immediately follows the last data field character is an asterisk.
• The asterisk is immediately followed by a two-digit checksum representing a hex number.
The checksum is the exclusive OR of all characters between the $ and the *. According
to the official specification, the checksum is optional for most data sentences, but is
compulsory for RMA, RMB, and RMC (among others).
• <CR><LF> ends the message.
As an example, a waypoint arrival alarm has the form:
$GPAAM,A,A,0.10,N,WPTNME*32 
where:
Table 12-2: NMEA data format
GP

Talker ID (GP for a GPS unit

AAM

Arrival alarm

A

Arrival circle entered

A

Perpendicular passed

0.10

Circle radius

N

Nautical miles

WPTNME

Waypoint name

*32

Checksum data

14.16 NO_EVENT
Occurs periodically (once per second by default). An application can use this event to perform
periodic status updates.
14.17 ORB_ANTENNA_VSWR
An ORBCOMM Antenna VSWR measurement result is available in 0.1 units (e.g. 15 => 1.5:1
VSWR).
14.18 POSITION_ALARM
A GPS measurement completed and a Geo-Fence violation occurred. The parameter indicates
which Sensor Table was used. This function is currently unsupported. Please contact QUAKE
Global if you would like to implement GEO_fencing in your product.