44 G12 OEM Board & Sensor Reference Manual
intentionally advanced or retarded). The latency of PBN message output is
normally about 40 milliseconds after the timing pulse event.
The timing pulse option [L] includes a secondary measurement strobe output on
pin 23 of 30-pin connector J301. The measurement strobe is also a TTL-level
square-wave signal fed into a 75-ohm impedance, and is also synchronized with
GPS time to an accuracy of ±1 microsecond. Output of the measurement strobe is
controlled by the $PASHS,STB command and is synchronized with GPS time.
The period depends upon the xxxx value and the setting of the RCI parameter.
The ±yyy.yyyy field allows you to set an offset value from GPS time with a
resolution of 100 nanoseconds, and also allows you to synchronize the rising or
falling edge of the output with GPS time. The accuracy of the measurement
strobe output is 0.5 milliseconds. For more information, see Chapter 4,
Command/Response Formats.
The G12 provides the optional capabilities of 10 Hz or 20 Hz internal update rates
for position and raw data computations. When these options are installed, the
G12 can output NMEA messages and raw data messages at intervals of 0.1 or
0.05 seconds (see Table 1.4 for a list of the available options). Because of power
limitations in the G12’s CPU, when the receiver is set to update position and raw
Figure 3.6. Relationship of GPS Time in PRN Record to 1PPS Pulse
G12RevD.book Page 44 Tuesday, April 2, 2002 4:33 PM
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