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Freeway
Range
Pro-Bel
ltd
5 Control system operation
The following sections describe the control system of
Freeway.
The control
module provides the
interfaces, database
and
software
to configure and control
the
Freeway
series routers
.
• 5. 1 Master and slave module details
The
Freeway
unit containing the plug-in control modules is designated MASTER
and all other units are designated SLAVES as they are slaved off the master using a
unidirectional parallel bus. Each of the main router units has level address select
switches that are used to identify each of the control levels.
Each router provides a module detect (handshake) mechanism so that the system
control module can detect the presence of various router units .
• 5.2 Master router dual control and
changeover
In a dual
-control
environment, one card is ACTIVE while the other is IDLE
.
In the
event of the ACTIVE controller failing, the IDLE controller will take over control
of the fram
e
and become ACTIVE.
On power up, the controller des
ignated
MASTER will also become ACTIVE. Every
main loop, the software checks whether a changeover has occurred
.
When a
controller changes state from IDLE to ACTIVE, or on power-up, a message is
issued to General Remote ports to report this fact. Thereby this information may
be relayed to an external control system such as a Pro-Bel System 3 controller. An
Editor s version message will also be displayed on the editor
terminal.
Both controllers contain identical data concerning the state of the
system.
This is
maintained by incorporating a serial link between them. Tally information is
requested on a background basis by the idle card.
Arbitrat
ion
ensures only the active card sets crosspoints.
6540T-00 Nov 97
42
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