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A-22 Acutime 2000 Synchronization Kit User Guide
Trimble Standard Interface Protocol
A
0x20 Command Packet 20
Almanac Request
This packet requests almanac data for one satellite from the GPS
receiver. This packet contains one data byte specifying the satellite
PRN number. The GPS receiver returns packet 40 hex.
0x21 Command Packet 21
Current Time Request
This packet requests current GPS time. This packet contains no data.
The GPS receiver returns packet 41 hex.
0x23 Command Packet 23
Initial Position (XYZ Cartesian ECEF) Command
This packet provides the GPS receiver with an approximate initial
position in XYZ coordinates. This packet is useful if the user has
moved more than about 1,000 miles since the previous fix.
!
Note – The GPS receiver can initialize itself without any data from the
user; this packet merely reduces the time required for initialization.
This packet is ignored if the receiver is already calculating positions.
The origin is the earth’s center. The X-axis points toward the
intersection of the equator and the Greenwich meridian, the Y-axis
points toward the intersection of the equator and the 90
o
meridian,
and the Z-axis points toward the North Pole. The cold-start default
LLA (not XYZ) position is 0, 0, 0.
The data format is shown in the table below.
Table A-19 Command Packet 23
Byte Item Type Units
0-3 X Single meters