Schneider Electric 840 USE 106 0 manual Command Register

Using a Quantum 984 HSBY System

Command Register

Command

Register

The State RAM Transfer Area

Nontransfer Area

Within the State

RAM Transfer

Area

CAUTION

Command Register Hazard

If you use the command register to enable the keyswitch override while the Hot Standby system is running, the Primary controller immediately reads bits 14 and 15 to determine its own state and the state of the Standby.

If both bits are set to 0, a switchover occurs and the former Primary CPU goes offline. The new Primary CPU continues to operate.

Failure to follow this precaution can result in injury or equipment damage.

The command register must be contained within the range of 4x registers in the state RAM transfer area.

A fixed block of up to 12K words in state RAM is specified as the transfer area. It consists of the following:

All the 0x discrete outputs in state RAM up to a maximum of 8192, including their associated histories

All the 1x discrete inputs in state RAM up to a maximum of 8192, including their associated histories

If the total number of registers (3x and 4x combined) implemented in state RAM

lis 10,000 or less, then all the registers plus the up/down counter history table

If the total number of registers (3x and 4x combined) implemented in state RAM is greater than 10,000, then a total of 10,000 is transferred, in accordance with the previously described formula. See Default Transfer Area, p. 38.

You also must define a nontransfer area in the middle node of the the CHS instruction block. A nontransfer area:

is a tool to reduce scan time

is located entirely within the range of 4x registers in the state RAM transfer area which are transferred on every scan

lconsists of a block of four or more 4x registers

allows the user to monitor the status of the Hot Standby system (third register of non-transfer area)

76 840 USE 106 00 January 2003