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4 Message Formats
MiLLennium GPSCard Software Version 4.50 Command Descriptions Manual Rev 1 47
NovAtel header and terminates with a checksum.
This message was designed so that
RTCA data can be intermixed with other NovAtel ASCII data over a common
communications port. The log is not in pure
RTCA format. The header ($RTCA) and terminator (*xx) must be
stripped off at the receiving end, then the data will need to be converted from hexadecimal to binary before the
RTCA information is retrieved.
The
RTCAA log can be directly decoded by other NovAtel GPSCard receivers operating as remote stations. They
will recognize the $
RTCA header as a special data input command and the differential corrections data will be
directly applied. The GPSCard remote station receiving this log must have the
ACCEPT command set to "ACCEPT
port COMMANDS".
Structure:
Example:
$RTCA,990000000447520607BE7C92FA0B82423E9FE507DF5F3FC9FD071AFC7FA0
D207D090808C0E045BACC055E9075271FFB0200413F43FF810049C9DFF8FFD074F
CF3C940504052DFB*20[CR][LF]
RTCAB
The
RTCAB log contains the SCAT-I differential corrections message with the standard NovAtel binary log preamble
(header) added. The
RTCAB log will be accepted by the GPSCard over a COM port after an "ACCEPT port RTCA"
command is issued.
Format: Message ID = 38 Message byte count = 12 + (11+(6*obs)): 95 bytes maximum
4.2 RTCM-FORMAT MESSAGES
The Radio Technical Commission for Maritime Services (RTCM) was established to facilitate the establishment of
various radio navigation standards, which includes recommended
GPS differential standard formats.
$RTCA data *xx [CR][LF]
Field # Field Type Data Description Example
1 $RTCA Log header $RTCA
2 data SCAT-I type 1 differential
corrections
990000000447520607BE7C92FA0B82423E9FE507DF5F3FC9
FD071AFC7FA0D207D090808C0E045BACC055E9075271FFB
0200413F43FF810049C9DFF8FFD074FCF3C940504052DFB
3 *xx Checksum *20
4 [CR][LF] [CR][LF]
Field # Data Bytes Format Offset
1 Sync 3 char 0
(header) Checksum 1 char 3
Message ID 4 integer 4
Message byte count 4 integer 8
2 – Message block identifier
– Reference station ID
– Message type
– Message length
6 12
3 – Modified z-count
– Acceleration error bound
2 18
4 – Satellite ID
– Pseudorange correction
– Issue of data
– Range rate correction
–UDRE
6 20
5 Next PRN offset = 26 + (6*obs) where obs varies from 0 to (obs-1)
6 CRC 3