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Using a Quantum 984 HSBY System
72
840 USE 106 00 January 2003
Configuration Extension
Controlling the
Hot Standby
System by
Configuration
Extension
With the Hot Standby configuration extension screens:
You can specify the parameters in the Hot Standby command register and
customize the state RAM data transfer between the Primary and Standby units to
help reduce scan time.
If you decide to control your system using the configuration extension, you still may
want to program a CHS instruction in ladder logic. The CHS instruction allows you
to use Zoom screens, which allows you to access and modify the command register
while the system is running.
Ladder Logic in a
Hot Standby
System
All ladder logic for Hot Standby functions should be in segment 1. Network 1 of
segment 1 is reserved exclusively for the CHS instruction block and ladder logic
directly associated with it.
program all ladder logic specific to Hot Standby functions in segment 1When the
Hot Standby system is running, the Primary controller scans all segments, while
the Standby controller scans only segment 1 of the configured ladder logic
program. This has very important implications with respect to the way you
configure system logic:
do not program I/O control logic in segment 1
do not schedule any I/O drops in segment 1
the Standby controller in a Hot Standby system must never execute I/O logic.
Note: If both a configuration extension and the CHS instruction are used, the
configuration extension controls the Hot Standby system. The only function of the
CHS instruction is to provide Zoom screens. The parameters in the configuration
screens are applied by the controllers at startup. Once the controllers are running,
the Zoom screens may be used to access and modify the command register. The
changes are implemented during runtime, and can be seen in the status register.
However, if the Hot Standby system is later stopped and then restarted, the
parameters specified in the configuration extension screens go back into effect.