Schneider Electric 840 USE 106 0 manual Configuration Extension, Hot Standby System by

Using a Quantum 984 HSBY System

Configuration Extension

Controlling the	With the Hot Standby configuration extension screens:
Hot Standby
System by	You can specify the parameters in the Hot Standby command register and
Configuration	customize the state RAM data transfer between the Primary and Standby units to
Extension	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.
	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.

Ladder Logic in a All ladder logic for Hot Standby functions should be in segment 1. Network 1 of

Hot Standby	segment 1 is reserved exclusively for the CHS instruction block and ladder logic
System	directlyl	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

ldo not schedule any I/O drops in segment 1

the Standby controller in a Hot Standby system must never execute I/O logic.

72 840 USE 106 00 January 2003