Navman 11 User Manual

Page 70

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

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