T801-4 Installation and Operation Manual
System Configuration
63
© 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.
Table 4.4
DIP switch settings with a single QS
2
RSU receiver
Switch
Description
State
Function
1
selects the external 1PPS
RS-485 input on
PORT B
on
on
enables the external 1PPS RS-485 input on
PORT B
;
configures the 1PPS VALID I/O signal line on
PORT B
as an input
off
disables the external 1PPS RS-485 input on
PORT B
;
enables the internal GPS receiver
2
selects the GPS receiver
off
on
external GPS receiver is selected
off
the 1PPS source set by DIP switch 1 is selected
3
a
controls the 1PPS RS-485
output on
PORT B
optional
on
the 1PPS output is always on
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 VALID alarm from the RSU
b
4
a
controls the 1PPS TTL
output
optional
on
the 1PPS output is always on
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 VALID alarm from the RSU
b
5
off
default
6
off
default
7
off
default
8
c
sets the signal type for the
1PPS VALID IN and 1PPS
VALID I/O input lines
optional
on
the 1PPS VALID signal is steady state
off
the 1PPS VALID signal is pulsed
a. When DIP switches 3 and 4 are on, the T801-4 1PPS outputs will not be disabled (via the VALID signal from the
RSU) when the GPS fix is lost. The continuous 1PPS signal from the RSU GPS receiver is always presented on the
T801-4 outputs, even if it is invalid. The maximum drift of an 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. When the T801-4 is operating with a QS
2
RSU system with version 3.00.00.00 and later firmware, the T801-4 is
configured with a pulse-stretcher on the VALID I/O line (achieved with DIP switch 8). This has the effect of applying
a
≈
28 second delay to the VALID signal from the RSU. This delay effectively “masks” any momentary losses of GPS
fix. This delay is not applied to a QS
2
RSU system with firmware earlier than version 3.
c. You must set DIP switch 8 off if you are using a QS
2
RSU with version 3.00.00.00 and later firmware because the
RSU provides a pulsed VALID signal (1 pulse/10 seconds). Set DIP switch 8 on if you are using a QS
2
RSU with
firmware earlier than version 3.
