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Using a Quantum IEC Hot Standby System
132
840 USE 106 00 January 2003
Hot Standby Status Register
Hot Standby
Status Register
The third register in the nontransfer area is the Hot Standby status register. Use this
register to monitor the current machine status of the Primary and Standby
controllers.
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).
Note: Bit 16 in Modicon convention (shown in the diagram above) is bit 0 in IEC
convention. Setting bit 16 means writing a 0x0001.
1 2 3 4 5 6 7 8 12 13 14 15 1691011
This PLC in OFFLINE mode =
This PLC running in primary mode =
This PLC running in standby mode =
01
01
11
01
01
11
The other PLC in OFFLINE mode =
The other PLC running in primary mode =
The other PLC running in standby mode =
1
0PLCs have matching logic =
PLCs do not have matching logic =
1This PLC’s switch set to B =
0This PLC’s switch set to A =
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
(Supported only with Concept 2.5 or higher)