Product specifications

Crescent Integrator’s Manual 28
reference station and the remote unit – typically an additional 1 m error per
100 miles. This error is often seen as a bias in positioning, resulting in a
position offset. The scatter of the receiver is likely to remain close to constant.
The RTCM SC-104 data output by the Crescent Vector is converted from the
RTCA SC-159 data broadcast by SBAS networks.
Appendix B - Resources contains the contact information should you wish to
purchase a copy of the RTCM SC-104 specification.
C ONFIGURING THE C RESCENT V ECTOR
All aspects of Crescent Vector operation may be configured through any serial port
with the use of NMEA 0183 commands. These commands are described in Chapter
6. The following items are user-configurable:
• Selecting the differential source (SBAS or external RTCM)
• Setting the baud rate of both communication ports
• Choosing which NMEA data messages to output on the serial ports and the update rate
of each message
• Setting the maximum differential age cut-off
• Setting the satellite elevation angle cut-off mask
F IRMWARE
The software that runs the Crescent Vector is often referred to as firmware since it
operates at a low level. The type of firmware within the Crescent Vector is for the
processor. This type of firmware may be upgraded in the field through Port A as new
revisions become available. The version of firmware installed on the Crescent Vector
may be determined through the $JI command.
C ONFIGURING THE D ATA M ESSAGE O UTPUT
The Crescent Vector features three primary bi-directional ports referred to as A, B
and C(in addition to its differential-only Port D). GPS data messages for all three
ports are easily configured by sending NMEA commands to the Crescent Vector
module through all of its communication ports (the output of Port B can be
configured through A, for instance and vice versa). The $JASC NMEA message
discussed in Chapter 6 in details allows you to turn messages on and off as you
require.
T HIS P ORT AND THE O THER P ORT
The NMEA interface for Port A and B both use ‘This’ and ‘Other’ terminology.
When interfacing to either port for the sake of turning data messages on or
off, the port that is being communicated with is referred to as ‘This’ port. If
you wish to turn a data message on or off, on the opposite port to which you
are communicating, the opposite port is referred to as the ‘Other’ port.