Schneider Electric 840 USE 106 0 manual State RAM Size

Using a Quantum IEC Hot Standby System

State RAM Size

State RAM Size

Note: The size of the configured state RAM in an IEC Hot Standby project has a significant impact on the system’s scan time. Once a logic scan is finished, the next does not start before all state RAM data has been transferred to the CHS module.

Once the number of IEC HSBY Registers has been set, you may deactivate the IEC Hot Standby configuration extension and activate it again later, the number of IEC HSBY registers remains the same.

The following diagram shows the IEC State RAM Map.

State RAM (compl. xferred)

0x			Header			Safety buffer
			(Exec vers.,		Program data	for future
Total						changes/
			timing info,...)	prog. data
					used	additions
1x				configured	Program data
Total
					unused
	IECforbufferheap		IEC heap
Total3x		No. 3x regs	Spaceas big as		DFB instance
					data
		configured for
		IEC HSBY
	Transfer

Total 4x

free memory for addtl. DFB instance data

134 840 USE 106 00 January 2003