Haicom HI-203E User Manual - page 10
3.4 O NE-PULSE-PER-SECOND (1PPS) OUTPUT
The one-pulse-per-second output is provided for applications requiring precise timing
measurements. The output pulse is 1usec in duration. Rising edge of the output pulse is
accurate to +/-1usec with respect to the start of each GPS second. Accuracy of the
one-pulse-per-second output is maintained only when the GPS receiver has valid position fix.
The 1PPS output is always generated when the GPS receiver is powered-on. Proper
adjustment of the 1PPS output to align with the GPS second requires calculation of the
receiver clock offset and clock drift-rate as part of the position-velocity-time (PVT) solution.
When enough satellite signals are received to generate valid position fixes, the 1PPS output is
adjusted to align with the GPS second in several seconds. When the 1PPS output is brought in
sync with the GPS second, the 1PPS Valid Signal on the I/O pin becomes active (HIGH); when
the 1PPS output is not yet in sync with the GPS second, the 1PPS Valid Signal remains
inactive (LOW).
As long as enough satellite signals are received to generate valid position fixes, the 1PPS
output remains synchronized to the GPS second, and the 1PPS Valid Signal remains active. If
signal blockage prevents the receiver from generating valid position fix, the 1PPS output will
drift away from the GPS second and the 1PPS Valid Signal will become inactive. Upon
re-acquiring enough satellites to generate consecutive valid position fixes, the 1PPS Valid
Signal will become active again, signaling that the 1PPS output is again synchronized with the
GPS second.
For best stable operation of the 1PPS signal, it is to be operated in static environment having
clear view of the sky.
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