Schneider Electric 840 USE 106 0 manual Updating Project, Global Data

Using a Quantum IEC Hot Standby System

Updating Project	With a logic mismatch, project global data will be updated with every scan. Global
Global Data	data that do not exist on both controllers is not updated.
	The project global data that is updated includes:

All variables declared in the Variable-Editor

lAll Constants declared in the Variable Editor All section and transition variables

Hot Standby behavior for project global data updating is:

All declared variable/constant will be updated every scan as long as they are declared on both controllers

If a complete download is done to the controller that did not receive the download change, then both controllers will have equal logic and therefore the Standby

lcontroller gets updated fully.

If, due to a download change, a project global variable/constant has been deleted first, and then redeclared, this variable/constant would be treated as a NEW variable/constant, even if the same name is used. The update procedure must be followed to bring the controllers to an equalized state.

Note: This is true whether these variables/constants are used in the controller program or not. Unused variables consume space and require time to be transferred from the Primary to the Standby controller. It is not recommended to have many variables that are defined but not used in the Primary controller program.

Nontransfer Area Although customizing transfers is not an option, you should designate a block of 4x

of State RAM registers as the nontransfer area. These registers are ignored when state RAM values are transferred from the Primary controller to the Standby. Placing registers in the nontransfer area is one way to reduce scan time because the Primary PLC to CHS transfer time is shorter. See State RAM, p. 129 for more detail.

126 840 USE 106 00 January 2003