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Chapter 3 - Receiver Descriptions

NMEA Protocol Support

The M12+ Positioning Receiver firmware supports the NMEA 0183 format for GPS data output.

Output of data in the NMEA-0183 standard format allows a direct interface via the serial port to

electronic navigation instruments that support the specific output messages. NMEA formatted

messages may also be used with most commercially available mapping and tracking programs.

The following NMEA output messages are supported as per the NMEA-0183 Specification

Revision 2.0.1:

Message Description

GPGGA GPS Fix Data

GPGLL Geographic Position Latitude/Longitude

GPGSA GPS DOP and Active Satellites

GPGSV GPS Satellites in View

GPRMC Recommended Minimum Specific GPS/Transit Data

GPVTG Track Made Good and Ground Speed

GPZDA Time and Date

You can enable or disable each message output independently and control the update rate at

which the information is output. The seven NMEA messages may be individually programmed to

be sent out continuously at any rate from once-per-second to once-every-9999 seconds, or may

be requested as individually polled responses.

If back-up power is applied or if the receiver has the battery option, the M12+ receiver retains the

output settings when powered off and reconfigures itself to the same state when powered up

again. If no back-up power is provided, the receiver will start up in the default state (Motorola

binary format at 9600 baud with all messages in the polled configuration) each time it is powered

on.

NMEA Commands to the Receiver

All NMEA commands are formatted in sentences that begin with the ASCII '$' character and end

with ASCII <CR><LF>. A five character sequence (PMOTG) occurs after the ASCII $, identifying

the command as a Proprietary MOTorola GPS command. The next three characters are the

sentence formatter (or message ID). The next four characters designate the update rate being

requested. The command is then terminated with an optional checksum and the normal Carriage

Return/Line Feed characters. Several examples are shown below. Note that unlike Motorola

binary messages, NMEA messages are not fixed length. Field widths within the message can

vary depending on the contained data, and are delimited by the ASCII comma character.

As noted above, checksums are supported in NMEA protocol, but are not required as they are in

the binary protocol. The checksum is calculated by XORing the 8 data bits of each character in

the sentence between, but not including, the $ and the optional (*) or checksum (CS). The high

and low nibbles of the checksum byte are sent as ASCII characters.

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Motorola M12 Oncore Guide de l'utilisateur Page 44