6 Message Formats

36 MiLLennium Command Descriptions Manual

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
6.2 RTCM-FORMAT MESSAGES
RTCM SC-104 Type 3 & 59 messages2 can be used for reference station transmissions in differential systems.
However, since these messages do not include information on the L2 component of the GPS signal, they cannot be
used with RT-2 positioning. Regardless of whether single or dual-frequency receivers are used, the RT-20
$RTCA data *xx [CR][LF]
Field # Field Type Data Description Example
1$RTCA Log header $RTCA
2data SCAT-I type 1 differential
corrections 990000000447520607BE7C92FA0B82423E9FE507DF5F3FC9
FD071AFC7FA0D207D090808C0E045BACC055E9075271FFB
0200413F43FF810049C9DFF8FFD074FCF3C940504052DFB
3*xx Checksum *20
4[CR][LF] [CR][LF]
Field # Data Bytes Format Offset
1Sync 3 char 0
(header) Checksum 1 char 3
Message ID 4 integer 4
Message byte count 4 integer 8
2– Message block idenifier
– Reference station ID
– Message type
– Message length
612
3– Modified z-count
– Acceleration error bound 218
4– Satellite ID
– Pseudorange correction
– Issue of data
– Range rate correction
– UDRE
620
5Next PRN offset = 26 + (6*obs) where obs varies from 0 to (obs-1)
6CRC 3