TrueTime VME-SG2 560-5608, Руководство пользователя

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Rev. F
d) Position Load - this bit (5) is used in conjunction with the Position Output
Disable bit described above. It generates a request to the VME-SG-GPS to
transfer the position information loaded by the user into the GPS Engine.
e) Negate Interval - Set bit 6 to clear the Interval output signal. This bit may
be set at any time the user wishes to guarantee that the Interval output is
negated or to abort a time coincidence operation when already in the interval
period. Bit 6 is automatically cleared when the Interval is cleared. This process
will generate a Stop pulse.
f) GPS Time Output Flag When the VME-SG-GPS card is in the GPS
Sync-gen mode, setting bit 7 will cause time outputs to reflect GPS time. When
bit 7 is a zero the card outputs UTC time. UTC time is affected by leap seconds.
GPS time will normally be several seconds ahead of UTC time and is not
affected by leap seconds.
POSITION MODE (base a hex 00A4)
This register is used to select the GPS Position Mode. The GPS Receiver will compute
position information if 4 or more satellites are available with a Vertical and Horizontal
Dilution of Precision (VDOP and HDOP) of 6 or less. If the position is known, time may
be determined with only one satellite. The Position Mode allows the user to determine
the manner in which the position of the antenna (latitude, longitude and elevation) is
determined. There are 4 modes available. Each mode with the value representing it in
the Position Mode registers is shown below:
Character MODE
------------------------------
0 -
Known
1 - Survey
2 - Automatic
3 - Dynamic
a. KNOWN - In the Known mode the current position will be held fixed. If
the user knows the position of the antenna it is entered via the Position registers
when in this Position Mode. Position data can be entered only while the Position
Mode is in the Known mode. If the unit is stationary this mode will provide the
best timing accuracy assuming the position is correct. When the position is
known only one satellite is necessary to determine accurate time.
b. SURVEY - In the Survey mode the GPS Receiver is directed to compute
position. There must be 4 satellites in view to calculate Latitude, Longitude and
Elevation. When only 3 satellites are available the Elevation will be held fixed at
the last computed value. The GPS Engine will compute position only when
HDOP and VDOP values are less than 6.
c. AUTO - The Automatic mode is a combination of the Survey and Known
Position modes. When the Auto Position mode is asserted the GPS Receiver is
placed in the Survey mode until accurate position with DOPs of 6 or less has
been computed. At that time the unit will automatically switch to the Known
mode, holding the current accurate position fixed. This mode makes it
unnecessary for the user to watch the unit to determine when good position has
been computed and then place the unit in the Known mode.
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