Novatel OM-20000041 用户手册

1

Quick Start

MiLLennium GPSCard Software Version 4.50 Command Descriptions Manual Rev 1

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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.

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.

Use the 

CDSA

/

B

 logs to monitor the COM port activity, success, and decoding errors.

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.

The 

CDSA

/

B

 logs may be used to monitor the COM port activity and differential data decode success.

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.

Before initializing, ensure that the data link with the reference station has been properly set up. As well, ensure that
the COM port which is to receive the differential data is set up to match the bit rate and protocol settings of the
reference station broadcast data.