Schneider Electric 840 USE 106 0 manual Example

Theory of IEC HSBY Operation

Example	This example shows the effect of a configuration change from baseline as shown in
	the IEC Scan Time Increase Table (See Overall PLC Scan Time, p. 49).
	A particular application has a standalone scan time of 25 ms in a PLC of type CPU
	434 12. The state RAM to be transferred consists of 200 coils (0x), 300 discrete
	inputs (1x), 150 input registers (3x), 400 holding registers (4x) and 14000 IEC HSBY
	registers (3x).
	The state RAM difference to the reference configuration is:
	Effects of a Configuration Change from Baseline
	0x
	200	- 1536 = - 1336	-1336*3/8	= - 501 Bytes
	1x
	300	- 512 = - 212	- 213*3/8	= - 80 Bytes
	3x
	150	- 512 = - 362	- 362*2	= - 724 Bytes
	4x
	400	- 1872 = - 1472	-1472*2 + ( - 1472*2/8)	= - 3312 Bytes

IEC Hot Standby regs 14000(3x) = 14000*2 = 28000 bytes Total = 28000 - 501 - 80 - 724 - 3312 = 23383 bytes Scan time offset = 23383*1.9ms ~ 44ms

This application therefore would have an overall scan time in Hot Standby:

40 ms (reference with CPU 434 12/ 534 14)

+25 ms (logic solve)

+44 ms (offset through memory increase) = 109 ms

50 840 USE 106 00 January 2003