Schneider Electric 840 USE 106 0 manual Example, Scan Time Increase Table in PLC Scan Times, p

	Theory of 984 HSBY Operation
Example	This example shows the effect of a configuration change from baseline as shown in
	the Scan Time Increase Table in PLC Scan Times, p. 34.
	A particular HSBY application has a standalone scan time of 36 ms in a PLC of type
	CPU 424 02. The state RAM to be transferred consists of 3000 coils (0x), 2500
	discrete inputs (1x), 2500 input registers (3x) and 8000 holding registers (4x).

The state RAM difference to the reference configuration is shown in the Effects of a Configuration Change from Baseline table below:

0x3000	- 1563 =	1464*3/8	=549 Bytes
1464
1x2500	- 512 =	1988*3/8	= 746 Bytes
1988
3x2500	- 1212 =	1288*2	= 2576 Bytes
1288
4x8000	- 1872 =	6128*2 + (6128*2/8)	= 13788 Bytes
6128

Total: 17659 bytes = scan time offset = 17659 * 1.6ms ~ 28ms

This application therefore would have an overall scan time in Hot Standby: 40 ms (reference with CPU 424 02 0x) added by HSBY

+36 ms (standalone scan time)

+28 ms (offset through configuration increase) =104 ms

Note: No matter how long your transfer takes, it does not cause a watchdog timeout.

840 USE 106 00 January 2003 35