3280-dda.ib.doc
page 11 of 16
23/07/2002
Operation:
Handshake mode detection:
Two data lines are present on the module rear connector to indicate to each module that it is to operate in handshake
mode.
The
Loop
signal on pin 16a is connected to ground when another module is connected and the
Present
signal on pin
16b detects the presence of power on the alternate module.
If the
Loop
signal is not connected to ground then all handshake operations are inhibited.
If the loop signal is at ground indicating the presence of an alternate module and if power is present on both modules
then normal handshake operation is permitted. If the
Present
signal indicates that power is lost on the alternate
module then the module with power will take control and become
Main
.
Power on reset.
When power is applied to the pair the
power on reset
signal will attempt to reset both modules. However, as only
one module can be
Main
, the logic processor checks for handshake operation and if detected then the module which
was last enabled as
Main
will take control as
Main
and the other module will be forced to act as
Reserve
.
This memory capability is due to the latching nature of the K 3 relay, which will cause the
Main
and
Reserve
paths
to be maintained even in the absence of power.
The only exception to this rule is when power is applied to a pair for the first time that they are coupled in
handshake mode. In this special case both modules will initially have their K 3 relays in the active path condition
and so both will attempt to become
Main
. As the P.O.R. signal for each module will be slightly different for any two
modules, one will reach its operating mode first and will force the other module to immediately change to become
Reserve.
As the selection of which module becomes
Main
is cannot be determined before installation it may be necessary to
force the desired module to become main by pressing the
Change Request
button on the front panel of the desired
module. The
Main
module will be indicated by the
In Service
LED, on the front panel, lighting.
Automatic changeover:
An automatic changeover is initiated whenever the power fails on
Main
and not on
Reserve
or when a general alarm
is initiated on
Main
(indicating either loss of input signal or AIS indication if the AIS is enabled) and the
Change
Inhibit
switch is not active on either module.
In either case, the
Main
Status
line will go from LO to HI. The companion module, on detecting this change, will
switch its
Main Select
line to HI. The K 3/1 relay driver then activates the relay (hence becoming
Main
) and sends
the
Status
line to the first module LO confirming the change and preventing that module from attempting to become
Main
again.
Manual changeover:
A manual changeover is initiated by pressing the
Change Request
button on the front of the module that is required
to become
Main
.
The mechanism of the change is similar to the automatic changeover described above except that it is initiated by
the module requesting that it become
Main
. This forces the
Status
line to the other module to LO and it immediately
responds to become
Reserve
.
IRT
Communications
www.irtcommunications.com