70
System Configuration
T801-4 Installation and Operation Manual
© Tait Electronics Limited September 2007
If both 1PPS signals become invalid:
■
The Satsync 7 module(s) will continue to use one of the 1PPS signals as
a reference for the frequency outputs.
■
The Satsync 7 oscillator alarms (and front panel LEDs) may or may not
be activated, depending on the accuracy of the free-running 1PPS signal
from the RSU GPS receiver.
■
The GPS alarms will
not
be activated. This is because 1PPS signal is still
present, and the 1PPS VALID signals from the RSUs are not available to
the Satsync 7 module(s).
If both 1PPS signals become invalid, it is extremely important that the
system is alerted by proper monitoring. A system alert can be raised by
monitoring the 1PPS VALID OUT output line (pin 9 of
PORT B
). This
line will go high (5V) when one (or both) of the 1PPS signals becomes
invalid. This line essentially reflects the 1PPS VALID signals from the RSU.
The T801-4 has no logic to advise whether one or both of the 1PPS inputs
is causing the 1PPS invalid condition. However, if required, you can use the
spare RSU Interconnect port (GPS signal interface) on the primary RSU
(refer to
Figure 4.6 on page 66
) to monitor which 1PPS signal has become
invalid. The appropriate pin allocations for this port are described in the
following table.
Table 4.8
Pin allocations on the QS
2
RSU Interconnect port - primary RSU
Pin
Signal Name
Signal Type
Notes
4
1PPS_VALID1
active low, 3V logic
VALID signal from primary RSU
5
1PPS_VALID2
active low, 3V logic
VALID signal from secondary RSU
6
DGND
common digital
ground return
1 2 3 4 5 6 7 8
external view
