T801-4 Installation and Operation Manual
System Configuration
53
© Tait Electronics Limited September 2007
DIP Switch Settings
Set the DIP switches on the rear panel as indicated in the following table.
Some switches have optional settings, depending on the requirements of
your particular system. Refer to
“DIP SWITCHES” on page 22
for full
details of all the DIP switches.
1PPS VALID IN
Set DIP switch 7 on if you want to use the 1PPS VALID IN line as an
external control input (in this situation you would also normally set DIP
switch 8 on). An internal pull-up resistor to 3.3V is provided on this input,
because it is designed to interface with the QS
2
RSU. The maximum
voltage on this input is 9V, and the line must be pulled to ground to indicate
a valid 1PPS signal. The line is activated when released from ground. The
input has no effect if a GPS alarm has already been activated.
Table 4.1
DIP switch settings with an internal GPS receiver
Switch
Description
State
Function
1
off
default
2
off
default
3
a
controls the 1PPS RS-485
output on
PORT B
optional
on
the 1PPS output is always enabled
off
the output is on only when the 1PPS signal is valid
(i.e. based on a GPS fix); the output will be
disabled by the GPS alarm (after the fault output
delay period
b
)
4
a
controls the 1PPS TTL
output
optional
on
the 1PPS output is always enabled
off
the output is on only when the 1PPS signal is valid
(i.e. based on a GPS fix); the output will be
disabled by the GPS alarm (after the fault output
delay period
b
)
5
off
default
6
off
default
7
controls the 1PPS VALID
IN input line
optional
on
the 1PPS VALID IN input is enabled
(could be used if an external signal is required to
control the 1PPS outputs - see
“1PPS VALID IN”
below)
off
the 1PPS VALID IN input is disabled
8
sets the signal type for the
1PPS VALID IN and 1PPS
VALID I/O input lines
optional
on
the 1PPS VALID IN signal is steady state
off
the 1PPS VALID IN signal is pulsed
a. When DIP switches 3 and 4 are on, a GPS alarm will not disable the T801-4 1PPS outputs. The continuous 1PPS
signal from the internal GPS receiver is always presented on the T801-4 outputs, whether or not the signal is based
on a GPS fix. The maximum drift of this invalid 1PPS signal could be quite large, therefore it should not be used
for precise synchronisation. Refer to
“1PPS Outputs” on page 33
for more information.
b. Refer to
“Fault Output Delay” on page 33
for more information.
