Schneider Electric 840 USE 106 0 manual Controllers, Supported only with Concept 2.5 or higher

Using a Quantum IEC Hot Standby System

Hot Standby Status Register

Hot Standby	The third register in the nontransfer area is the Hot Standby status register. Use this
Status Register	register to monitor the current machine status of the Primary and Standby
	controllers.
		This PLC in OFFLINE mode =						0	1
		This PLC running in primary mode =						1	0
		This PLC running in standby mode =						1	1
		The other PLC in OFFLINE mode =				0	1
		The other PLC running in primary mode =				1	0
		The other PLC running in standby mode =				1	1
		PLCs have matching logic =			0
		PLCs do not have matching logic =			1
	(Supported only with Concept 2.5 or higher)
		This PLC’s switch set to A	=	0
		This PLC’s switch set to B	=	1

1 2 3

4 5 6 7

8 9 10 11 12 13 14 15 16

	The CHS interface is healthy =	0
	An interface error has been detected =	1
Hot standby capability has not been activated			=	0
	Hot standby is active		=	1

Note: Bit 16 in Modicon convention (shown in the diagram above) is bit 0 in IEC convention. Setting bit 16 means writing a 0x0001.

IEC Heap Size As described in Theory of IEC HSBY Operation, p. 43, the IEC Heap is transferred from the Primary to the Standby controller through a reserved partition of state RAM. This partition consists of a contiguous block of 3x registers, they are the so called IEC HSBY Registers. Since they are part of state RAM, they are never more than 64K words (128 KByte). To ensure full data consistency in case of a switchover, all data of the Primary’s IEC application must be transferred to the Standby in every scan. The IEC heap, which contains all the to-be-transferred data, may not be bigger than the transfer buffer that carries the IEC heap from the Primary to the Standby controller (64K words).

132 840 USE 106 00 January 2003