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MN002000A © 2004 Navman NZ Ltd. All rights reserved. Proprietary information and specifications subject to change without notice.
Ephemeris data has been collected by the
receiver for at least four satellites.
DGPS corrections have been received for
at least the same four satellites, and these
corrections are not older than the time limit
specified in the Differential GPS Control
message (binary Message 1214)
The Issue Of Data Ephemeris (lODE) is the
same for both the receiver-collected ephemeris
and the RTCM SC-I04 corrections.
All of the applicable satellites have good health
or have been declared healthy for DGPS
purposes by the RTCM SC-I04 source.
The User Differential Range Error (UDRE)
reported by the RTCM SC-I04 source is equal
to or less than 8 m for all four satellites.
The RTCM SC-I04 source declares itself to be
in good health.
The user has not turned DGPS operation off.
4.7.4.5 Disabling DGPS operation
The user may disable DGPS operation through
the Differential GPS Control message (binary
Message 1214). When disabled the receiver will
not use DGPS information to compute a position
solution nor will the information be erased.
During the time that DGPS operation is disabled,
and DGPS solutions are not being computed,
RTCM processing continues as long as RTCM
messages are being sent to the receiver. The data
contained within these messages will be used to
update the receiver’s internal DGPS database. As
soon as the DGPS function is enabled, the most
current data will be used to compute a position
solution.
4.7.4.6 DGPS reset
The user may also “reset” the DGPS process
at any time using the Differential GPS Control
message (binary Message 1214). When this
is done, the DGPS data currently stored in the
receiver is invalidated or replaced by its default
values. This discontinues DGPS service until new
RTCM SC-I04 and ephemeris data is collected.
A DGPS reset is different from the type of reset
initiated by power-on or an initialisation message
system reset. During a DGPS reset, ‘DGPS
disable’ and ‘correction timeout’ are unaffected.
If values have been previously entered for these
words, these same values will be in effect both
before and after the DGPS reset. If new valid
entries for these words are received within a
DGPS control message that also contains a reset,
then the new values will be in effect after the reset.
However, after a DGPS reset all other DGPS
parameters will be set to their default values.
4.7.4.7 DGPS status request
The user may request that the status of DGPS
operation be provided. When requested, the DGPS
status message (binary Message 1005) provides
information on the state of each of the corrections
being processed. In the event that DGPS solutions
are not available, the status message also
provides enough diagnostic data for the user to
determine why they are not being computed.
4.7.5 Built-In Test (BIT)
The receiver can be commanded to execute a BIT
at any time while in Navman binary mode. The
receiver performs the test and returns the results
in the corresponding output message.
A BIT is commanded by sending a binary ‘perform
built-in test command’ message (Message 1300).
Such a command will interrupt normal receiver
operations and result in a system reset.
Output messages that are processed by the serial
I/O hardware when the BIT command is received
are output, but subsequent output messages are
suspended until after the BIT cycle is complete.
When the BIT is complete, the receiver is reset
and normal operation resumes. This means that
the BIT results may not be the first received output
message after a BIT command.
4.7.5.1 Interpreting BIT results
A device failure indicator in the ‘BIT results’
message is valid for all devices installed on the
board. The failure words defined in Message 1100
will be zero if the device is working as expected
and non-zero if an error was detected.
ROM failure
The ROM Failure word in Message 1100 indicates
the result of a ROM (program memory) checksum
test. A failed status means that the ROM chip may
be defective.
RAM failure
The RAM failure word in Message 1100 indicates
the results of a non-destructive pattern test and an
address line integrity test. A failed status means
that the RAM chip(s) may be defective.
EEPROM failure
There are no explicit tests of the EEPROM device
in response to message 1100. However, the
receiver maintains and reports a status of what
parameters have been written to EEPROM. When
a data block has been written and cannot be
successfully read back from the device, a failure
will be reported. A failure will also be reported
if the device does not respond to an attempt to