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C NMEA-0183 Messages
80 AgGPS 332 GPS Receiver User Guide
C2.2 Checksum values
Newer Trimble receivers conform to the NMEA-0183 Version 2.1 format,
in which checksums are mandatory for all messages.
The checksum is calculated from all characters in the message,
including commas but excluding the “$” and “*” delimiters. The
hexadecimal result is converted to two
ASCII characters (0–9, A–F), of
which the most significant appears first.
C2.3 Field formats
The data values output by Trimble AgGPS receivers meet the
NMEA-0183 Version 2.1 standard.
C2.4 Null fields
If a message contains a fixed number of fields, null (empty) fields are
included if no data is available. These fields are usually reserved for
data that is transmitted on a periodic or irregular basis.
C2.5 Talker ID codes
Talker ID code identifies the source of the data (for example, GPS,
Loran C, or Sounder). Table C.2 describes the Talker ID codes that are
available for
NMEA-0183 output from most Trimble receivers.
Table C.2 Supported Talker ID codes
Code Description
GP GPS
LG Loran C/ GPS
LC Loran C
II Integrated Instrumentation