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Basic Operation
33
Basic Operation
The Daisy-Chain mode establishes a communication link through the GPS
receiver, between a PC or handheld and a peripheral device. When the GPS
receiver is in Daisy-Chain mode, all commands entering one serial port are
passed out through another serial port. The commands are not interpreted by the
DG16. Use the
$PASHS,DSY
command to enable the Daisy-Chain mode and
assign which serial ports to use.
A typical example of the use of Daisy-Chain mode is communicating with a radio
through a handheld. The radio and handheld are not directly connected, but both
are connected to the DG16 via separate serial ports. By enabling the Daisy-Chain
mode between the two serial ports used by the handheld and radio, the handheld
can communicate with the radio through the DG16.
For more information on the Daisy-Chain command, see ”DSY: Daisy Chain
Communications Mode” on page 105.
When the DG16 is powered on for the first time, or when the power and back-up
battery have been disconnected, there is no almanac or ephemeris data in
memory. In these cases, the DG16 assigns the first 12 elements of a 32-element
table of SV PRN numbers to its 12 channels as it begins searching for satellites. If
no ephemeris data are in memory, or if the data are older than ten hours, 30 to 60
seconds are needed to collect data. The DG16 synchronizes its clock to GPS time
within six seconds of locking a satellite. After three or four satellites are locked
and the almanac and ephemeris data are collected, the DG16 computes its first
position. The DG16 continuously updates almanac, ephemeris, and position data
in its battery-backed memory to help optimize satellite requisition and time to first
fix when the unit is next powered on.
With the SBAS option installed, the DG16 tracks two geostationary SBAS
satellites at a time and makes the ranging ephemeris and SBAS differential
correction data messages available over ports A and B. The two SBAS satellites
tracked are based on the mode of operation selected by the user. If the Automatic
mode is selected, the DG16 automatically searches for and tracks the SBAS
satellites in a predefined order. If Manual mode is selected, the DG16 searches
for and tracks the SBAS satellites you selected. The search time for each satellite
should not exceed one minute for a hot start and three minutes for a cold start.
At the next power-up, if the almanac and ephemeris data are available in battery-
backed memory, and if the ephemeris data are less than ten hours old, the DG16
restricts its satellite search to those satellites that should be visible based on this
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Страница 105: ...Coordinate Transformation 85 Coordinate Transformation Figure 4 4 Oblique Mercator Figure 4 5 Stereographic...
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Страница 389: ...369 Index W warm start 2 33 WGS 72 81 WGS 84 4 81 86 X XMG 284 XYZ 221 Z ZDA 285...
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