Schneider Electric 840 USE 106 0 manual Switchover, Modbus Plus, Port Address, Swapping at

Using a Quantum 984 HSBY System

Swap Address at In a Hot Standby system, the Modbus ports on the Primary controller may have

Switchover	MEM addresses in the range of 1 to 119. This allows an offset of 128 for comparable
	ports on the Standby controller, with 247 the maximum number of addresses.
	For example, if controller A is the Primary controller and its two Modbus ports have
	addresses 1 and 2, then the default addresses for the comparable ports on Standby
	controller B are 129 and 130. By default, this offset is maintained between port
	addresses in the event of switchover. For example, if controller B becomes the
	Primary controller as the result of switchover, its Modbus ports assume the
	addresses of 1 and 2, and the comparable ports on controller A assume addresses
	129 and 130.
	The check boxes allow you to change this default condition on any or all of the
	Modbus ports on the two controllers in your Hot Standby system.
	Modbus ports on the two controllers in your Hot Standby system. For example: if you
	deselect the parameter Modbus Port 1, then no offset is maintained at switchover
	and after switchover the two ports have the same address. Thus if controller A is the
	Primary controller and its Modbus port 1 address is 1, then that port address remains
	1 after a switchover occurs. Likewise, if controller B becomes the Primary controller
	as a result of switchover, its Modbus port 1 address is also 1.
	Note: If you change the selections, the port addresses are not affected until a
	switchover occurs.
Modbus Plus
	In a Quantum Hot Standby system, the Modbus Plus port addresses on the Standby
Port Address	controller are offset by 32 from the comparable ports on the Primary controller. For
Swapping at	example, if controller A is the Primary controller and its Modbus Plus port has
Switchover	address 1, then the address for the corresponding port on Standby controller B is 33.
	The numerical range for addresses for both ports is 1 through 64. Thus, if the port
	on the Primary controller has address 50, then the address for the corresponding
	port on the Standby cannot be 82, so it is 18 (that is, 50 minus 32).
	These addresses are automatically swapped at switchover; you do not have the
	option to change the offset or prevent the addresses from being swapped.
	Note: The Quantum Hot Standby system swaps Modbus Plus addresses almost
	instantaneously at switchover. This means that host devices polling the Quantum
	controller can be assured that they are always talking to the Primary controller and
	that the network experiences no downtime during switchover.

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