Schneider Electric 840 USE 106 0 manual Synchronizing Time-of-Day Clocks, Synchronization

Using a Quantum 984 HSBY System

Synchronizing Time-of-Day Clocks

Clock	In a Hot Standby system, the Primary and Standby controllers have their own time-
Synchronization	of-day clocks. They are not synchronized. At switchover, the time of day changes by
	the difference between the two clocks. This could cause problems if you are
	controlling a time-critical application.
	To solve this problem, program the Standby controller to reset its clock from the
	state table provided by the Primary controller. If you are controlling your system via
	configuration extension screens, put the logic for time synchronization first.
	Otherwise, put the logic for time synchronization in segment 1, but do not put it in
	network 1.
	Since both controllers run the same program, you must read CHS status register bits
	12...16 to be sure that only the standby clock is resetting. If bits 12...16 are 01011,
	you know three things:

which controller is the Standby

lthat the remaining controller is the Primary that both controllers are running the same logic

If these conditions are true, then the logic should clear bit 2 and set bit 1 of the time- of-day control register. The clock in the Standby controller will be reset from the state table of the Primary controller at the end of a scan and bit 1 will be cleared.

Note: Be sure that the registers for synchronizing the time-of-day clocks are included in the state RAM transfer area.

106 840 USE 106 00 January 2003