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22 MiLLennium GPSCard SW Version 4.503/4.52 Command Descriptions Manual Rev 2
USING RTCM SC-104 LOG TYPES
RTCM SC-104 is a standard for transmitting differential corrections between equipment from different
manufacturers. The NovAtel GPSCard is capable of transmitting or receiving RTCM data.
To facilitate transmitting the RTCM data over shared data links, the GPSCard is also capable of sending the RTCM
log in NovAtel ASCII format (RTCMA) or with the NovAtel binary header (RTCMB) added to allow synchronous
transmission and reception along with other data types.
NOTE: When sending or receiving RTCM log types, it is important to ensure that all connected equipment are
using the same RTCMRULE for compatibility.
The easiest method to send RTCM standard logs is from the COM1 or COM2 ports of the reference GPSCard. The
easiest method to receive the RTCM data is through the COM1 or COM2 port of the rover GPSCard. The rover
GPSCard must issue the “ACCEPT port RTCM” command to dedicate a port before it will accept the RTCM data
into that port.
The RTCMA log can be intermixed with other NovAtel ASCII data over a common communication port. It will
be directly interpreted by a rover GPSCard as a special data input command ($RTCM). “ACCEPT port
COMMANDS” must be used with this input command. A non-NovAtel rover station will need to strip off the
header ($RTCM) and terminator (*xx), then convert the hexadecimal data to binary before the RTCM standard data
can be retrieved.
The RTCMB log can be intermixed with other NovAtel binary data over a common communication port.
REMEMBER: Use the CDSA/B logs to monitor the COM port activity, success, and decoding errors.
USING RTCA LOG TYPES
The RTCA (Radio Technical Commission for Aviation Services) Standard is being designed to support
Differential Global Navigation Satellite System (DGNSS) aviation applications. The perceived advantage to using
RTCA type messages for transmitting and receiving differential corrections versus using RTCM type messages is
that RTCM transmits 30-bit words, and the data is difficult to decode and process because of the parity algorithm
and irregular word sizes used. RTCA is transmitted in 8-bit words, which are easier to generate, process and
decode. The RTCA messages are therefore smaller, they have a 24 bit CRC that is much more robust than RTCM
messages, and they permit the use of a four-alpha-character station ID.
RTCA standard logs can be received through the COM1 or COM2 port of the rover GPSCard. The remote
GPSCard must issue the “ACCEPT port RTCA” command to dedicate a port before it will accept the RTCA data
input to that port. The RTCA logs cannot be intermixed with other logs.
The RTCAA log can be intermixed with other NovAtel ASCII data over a common communications port. It will
be directly interpreted by a rover GPSCard as a special data input command ($RTCA). “ACCEPT port commands”
must be used with this input command. A non-NovAtel rover station will need to strip off the header ($RTCA) and
terminator (*xx), then convert the hexadecimal data to binary before the RTCA standard can be retrieved.
The RTCAB log can be intermixed with other NovAtel binary data. The remote GPSCard identifies the RTCAB
log by the message block identifier contained in the message, and will interpret only the RTCA data portion of the
log.
NOTE: The CDSA/B logs may be used to monitor the COM port activity and differential data decode success.
Initialization - Rover Station
It is necessary to initialize the rover receiver to accept observation data from the reference station. If the receiver
is not correctly initialized, it will proceed to compute solutions in single point positioning mode.