T801-4 Installation and Operation Manual
System Configuration
59
© 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.
Alarms During
Power-up
Because of the time it takes the GPS receivers to acquire a fix, especially the
Dalman external GPS receiver (refer to
“GPS Fix Acquisition Times” on
page 31
), it is very probable that an alarm condition will occur after power-
up, but before a fix is acquired. This is quite normal. If DIP switch 5 is set
on during this alarm period, a “false” changeover event will occur. If this
does happen, set DIP switch 5 off, wait until the oscillator alarm has been
released, then switch it back on.
Note
To avoid confusion, we recommend that you set DIP switch 5 on
only after the alarms have been released.
Table 4.3
DIP switch settings with internal and external GPS receivers
Switch
Description
State
Function
1
off
default
2
selects the primary GPS
receiver
optional
on
external GPS receiver is selected
off
internal GPS receiver is selected
3
a
controls the 1PPS RS-485
output on
PORT B
n/a
the 1PPS output is always enabled
4
a
controls the 1PPS TTL
output
n/a
the 1PPS output is always enabled
5
on
default
6
b
selects the GPS changeover
alarm trigger
optional
on
the GPS receiver changeover is triggered only by
an oscillator alarm
off
the GPS receiver changeover is triggered by both
oscillator and GPS alarms
7
off
default
8
off
default
a. The 1PPS output may be invalid or disabled during the fault output delay period, before the GPS alarm activates
the changeover (refer to
“Fault Output Delay” on page 33
). The state of the T801-4 1PPS outputs during the fault
output delay period depends on which GPS receiver is the primary unit, and the fault condition that initiated the
changeover.
b.
Do not
trigger a changeover by “oscillator alarms only” if your system depends on the T801-4 1PPS outputs. As
described in
“Invalid GPS Reference” on page 30
, the loss of the GPS fix could mean the Satsync 7 VCO is “frozen”
and the oscillator alarms are delayed for 24 hours. The 1PPS outputs would therefore be disabled or invalid for
this 24 hour period.
