Novatel OM-20000077 Manuel D’Utilisation

The chapter discusses the industry-standard message formats that can be used with your SUPERSTAR II 
receiver, including RTCM and NMEA. Refer to the L1 GPS Firmware Reference Manual for more information 
on using these message formats.

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.

The standards recommended by the Radio Technical Commission for Maritime Services Special Committee 
104, Differential GPS Service (RTCM SC-104,Washington, D.C.), have been adopted by NovAtel for 
implementation into the receiver. Because the receiver is capable of utilizing RTCM formats, it can easily be 
integrated into positioning systems around the globe.

As it is beyond the scope of this manual to provide in-depth descriptions of the RTCM data formats, it is 
recommended that anyone requiring explicit descriptions of such, should obtain a copy of the published RTCM 
specifications. See Appendix D, Standards/References on Page 62 for reference information.

Message ID# 83, DGPS Configuration contains one or part of a RTCM message. The message type selected in 
the Set DGPS Configuration message (Message ID# 83, bytes 9 to 16) is retransmitted through this message. 
Message length is variable and a message can be transmitted up to once every 100 ms. A RTCM message 
always starts as the first byte of a message and always ends as the last byte of a message. Thus, a RTCM 
message can be output in one or many messages but a message block cannot contain more than one RTCM 
message. The control byte is used to determine the start and the end of a RTCM message. The sequence 
number of the control byte can be used to detect the loss of a message block on the transmitter side. It starts at 
0 and increments by one for each consecutive message block (0,1,2,3,0,1,2,3,0,1,...). Refer also to the L1 GPS 
Firmware Reference Manual for details on this message.

All receiver messages adhere to the structure recommended by RTCM SC-104. Thus, all RTCM messages are 
composed of 30 bit words. Each word contains 24 data bits and 6 parity bits. All RTCM messages contain a 2-
word header followed by 0 to 31 data words for a maximum of 33 words (990 bits) per message.

The remainder of this section will provide further information concerning receiver RTCM data formats.

This is the primary RTCM message used for pseudorange differential corrections. This message follows the 
RTCM Standard Format for a Type 1 message. It contains the pseudorange differential correction data 

Word 1

–

Message frame preamble for synchronization

8

–

Frame/message type ID

6

–

Base station ID

10

–

Parity

6

Word 2

–

Modified z-count (time tag)

13

–

Sequence number

3

–

Length of message frame

5

–

Base health

3

–

Parity

6