Orion NMEA User Manual
GPS Receiver Module
Micro Modular Technologies Pte. Ltd.
Page 1 of 25
No. 3, Ubi Avenue 3, #03-02 Crocodile House 408857 Singapore
Tel: 65-6745-8832 Fax: 65-6293-0661 Email: sales@micro-modular.com
www.micro-modular.com
1
Overview
This document describes the format and usage of NMEA messages for Orion GPS navigation
software. It also details the implementation specifics of NMEA input commands and output
sentences supported by Orion.
2
Message Format
Orion NMEA messages conform to the NMEA-0183 Ver. 3.01 (January 1, 2002) standard with
implementation specifics as noted below.
Commands start with a dollar-sign (“$”), followed by “PUNV”, and a comma (“,”). The command text
(which is defined in section 4) comes next, followed by an asterisk (“*”), two-digit hexadecimal
checksum, and the <carriage return> <new line> characters.
Example:
$PUNV,<command>*cc<carriage return><new line>
2.1
Checksum Calculation
In accordance with NMEA-0183, the checksum is calculated by taking the 8 bit exclusive OR of all
characters between (but not including) the “$” and the “*”. The checksum is then appended after the
“*” as a 2 character hexadecimal number.
If a command’s checksum is omitted or illegal the command will be rejected and an error message
issued.
A command with the checksum value “cc” (two lower case “c” characters) will be accepted as valid
(this is primarily used for testing purposes).
2.2
Sentence Termination Delimiter
All sentences end with the sentence termination delimiter <carriage return><new line>. This
combination is “\r\n” in C-language format and hexadecimal ASCII values are 0Dh 0Ah. Both
characters are required for a command to be recognized.
2.3
NMEA Message Sizes
In accordance with NMEA-0183, the maximum number of characters between the starting delimiter
“$” and the terminating <CR><LF> should be 79. That is, the maximum needed buffer size should be
82 for one output sentence.
For input NMEA commands, the maximum size accepted is 128 characters.
