TrueTime VME-SG2 560-5608, Manual

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2.4.7 READING POSITION
When in the GPS synchronized generator mode position information is generated by the
GPS Engine. Position consists of latitude and longitude in degrees, minutes, seconds
with North/South/East/West indicators and elevation in meters above or below sea level.
The position information actually defines the location of the antenna.
Position data is read at address offsets hex 90 - 9E. All values are packed BCD except
for the North/South and East/West indications which are ASCII byte values. Table 2-3
below describes each position register with its address offset and data organization.
Table 2-3, Position
2.4.8 LOADING POSITION
When in the GPS synchronized generator mode the position of the antenna is loaded
using the position registers described above. It is sometimes advantageous to load the
position of the antenna since accurate antenna position will reduce timing errors.
Accurate time is computed if only one satellite is tracked when the position information
is known. Due to buildings or other physical obstruction 4 or more satellites may not be
in view with great enough regularity to allow the VME-SG-GPS card to compute position
conveniently.
The Position Computation Mode must first be set to KNOWN so the GPS Engine will
stop computing new position data. In all modes the position is output to the registers
described above except when the Position Update Inhibit bit is set. This bit is contained
in configuration register #2, bit #4. This bit allows the registers to be used for loading
new position from the VME bus.
0090 Latitude
(0, Hund, Tens, Units degrees)
0092 Latitude
(Tmin, Umin, Tsec, Usec)
0094 Latitude
(N/S, Tenths seconds)
0096 Longitude
(0, Hund, Tens, Units degrees)
0098 Longitude
(Tmin, Umin, Tsec, Usec)
009A Longitude
(E/W, Tenths Seconds)
009C Elevation
(Sign, Ten Thous & Thous Meters)
009E Elevation
(hund, Tens, Unit and Tenths Meters)
** The right most value is in the least
significant nibble of the 16 bit word.
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