CG1-RADIO • CompactPCI GPS Receiver/Clock
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EKF Elektronik GmbH * Philipp-Reis-Str. 4 * D-59065 HAMM (Germany)
Tel. +49 (0)2381/6890-0 * Fax. +49 (0)2381/6890-90 * E-Mail
[email protected] * Internet http://www.ekf.de
The highly integrated digital GPS receiver
uses the Zodiac chip set (Rockwell/Conexant)
and is accommodated on a miniature
daughter board as an exchangeable sub-
assembly. The 12-channel architecture
provides rapid Time-To-First-Fix (TTFF) under
all startup conditions. The receiver decodes
and processes signals from all visible GPS
satellites, thereby producing a highly
accurate and robust navigation solution. The
external GPS antenna connects to the front
panel mounted SMB style jack and must
have reasonable visibility of the sky. For best
performance, use an active antenna,
especially for a cable length of 3m and
above.
Due to Selective Availability (SA) the GPS
navigation accuracy is limited to 100m for
civil use. The CG1-RADIO however as an
option allows to read in an external
differential signal (DGPS) in order to reduce
the positioning error to 3-5m. For this, the
CG1 is provided with a 9-pin D-SUB
connector (front panel) serial interface port.
Incoming DGPS data must conform to the
international RTCM SC-104 protocol. The
type of the external DGPS receiver depends
on the location. In Germany e.g. there is a
choice between the LW ALF transmitter
(Mainflingen, Deutsche Telekom) or the
RASANT FM RDS System (ARD).
Equipped with the powerful embedded
processor i960RP(D), the board profits from
the built-in PCI bridge as interface to the
CompactPCI
®
system bus. For typical
applications, the EKF software drivers let the
CPCI system host view the CG1-RADIO
module as 16C550 UART based dual serial
adapter card. Available by download, the EKF
utility WinGPS displays the GPS data and
allows for synchronization of the system
clock to the UTC.
The first serial port of the CG1-RADIO is for
on-board use only. It serves as a
communications interface to the GPS
receiver. Commands and data can be sent to
and received from the GPS daughter board
according to the NMEA-0183 standard
protocol. The moderate transmission rate of
4800bps cares for low interrupt load of the
system host.
The second serial port is intended either as
external DGPS interface (read only), or as a
general purpose RS-232E communications
channel. The wiring of the front panel
mounted 9-pin male D-SUB connector SP2 is
identical to desktop PC COM ports. When
receiving differential DGPS data at 9600bps
according to the RTCM SC-104 standard, the
GPS daughter module uses this information
for its internal calculations to sharpen the
positioning data. The second serial interface
is also directly readable by the system host.
Programs as LabMon (Rockwell/Conexant)
need DGPS data in parallel to the GPS
receiver for presentation.
If the DGPS data capability of the CG1-
RADIO is not used, then the serial port SP2
is available for general purpose I/O
applications.
The EKF drivers treat the CG1-RADIO module
as 16C550 compatible COM ports. While
the drivers allow arbitrary names e.g.
COM11, practically there exist limitations in
most systems. Typically, COM1 and COM2
are reserved names for the host CPU’s serial
interfaces. On the other hand, most GPS and
communications applications will support
COM1..4 only. Therefore COM3 is
recommended to control the GPS NMEA port
(first serial interface of the CG1-RADIO), and
COM4 to be used as DGPS RTCM receiver
(second serial port, SP2).
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