Hot Standby Command Register

Setting the Bits in the Command Register

The Command Register (System Word), %SW60, defines the operating parameters of a Hot Standby application for both the Primary CPU and Standby CPU.

At each scan, the Command Register is replicated and transferred from the Primary CPU to the Standby CPU. Transfer occurs only from Primary CPU to Standby CPU. Any changes made to the Command Register on the Standby CPU has no effect because the values transferred from the Primary CPU overwrite the values in the Standby CPU.

The following illustration identifies the operating options provided by the Command Register:

System Bit %SW60.0

Invalidate Keypad is an option that allows a controller to refuse commands from the Hot Standby submenu in the front panel keypad.

%SW60.0 = 1

Invalidate Keypad enabled.

The Quantum Hot Standby system refuses all changes from the Hot Standby submenu in the front panel keypad.
%SW60.0 = 0

Invalidate Keypad disabled.

The Quantum Hot Standby system accepts all changes from the Hot Standby submenu in the front panel keypad.

System Bit %SW60.1

Controller A OFFLINE/ONLINE mode:

%SW60.1 = 1

Controller A goes to the ONLINE mode.
%SW60.1 = 0

Controller A goes to the OFFLINE mode.

System Bit %SW60.2

Controller B OFFLINE/ONLINE mode:

%SW60.2 = 1

Controller B goes to the ONLINE mode.
%SW60.2 = 0

Controller B goes to the OFFLINE mode.

NOTE: The Primary CPU controller goes to RUN OFFLINE only if the secondary CPU is RUN Standby.

At Startup of the Secondary PLC, the secondary CPU goes to ONLINE mode (RUN Standby) only if both bits %SW60.1 and %SW60.2 are set to 1 (regardless of A/B assignment).

If bits %SW60.1 and %SW60.2 are set to 0 simultaneously, a switchover occurs:

the Primary CPU controller goes to the RUN OFFLINE mode
the Standby CPU goes to the RUN Primary CPU mode

To complete the switchover, bits %SW60.1 and %SW60.2 must be set back to 1. This makes the Offline CPU go back to the online RUN Standby mode.

The OFFLINE/ONLINE modes controlled by %SW60.1 and %SW60.2 are not linked to the LCD Keypad ONLINE/OFFLINE mode.

WARNING

UNEXPECTED EQUIPMENT BEHAVIOR

Ensure that your system does not switchover from the application program before starting a CCOTF modification.

Failure to follow these instructions can result in death, serious injury, or equipment damage.

System Bit %SW60.3

Application mismatch:

%SW60.3 = 0

If an Application mismatch is detected, Standby CPU is forced to OFFLINE mode.
%SW60.3 = 1

Standby CPU operates normally even if a mismatch occurs.

System Bit %SW60.4

Firmware upgrade:

%SW60.4 = 1

Allows the firmware to be upgraded on the Standby CPU, while the Primary CPU continues to control the process.
%SW60.4 = 0

Allows the firmware to be upgraded and stops the Primary CPU control of the process.

Upgrading allows:

a Hot Standby system to operate with different versions of the OS running on the Primary CPU and Standby CPU
upgrades without shutting down the process

To perform the firmware upgrade, the Standby CPU must be stopped. When started again, the Standby CPU operates again as the Standby CPU.

System Bit %SW60.5

Standby CPU initiates an application transfer:

%SW60.5 = 1 means Standby CPU requests an application program transfer from Primary CPU
%SW60.5 = 0 is default and no transfer occurs

NOTE: %SW60.5 is a Monitor Bit.

%SW60.5 monitors an action. Once the action occurs, %SW60.5 returns to the default, which is zero (0).

NOTE: In the case of ONLINE application mismatch selected, the Hot Standby system needs 2 seconds to check the consistency of the application and the detection of an application mismatch (%SW61.4). Therefore the request for application transfer (%SW60.5) has to be done with a minimum delay of 2 seconds after any modification of the application.

WARNING

UNEXPECTED BEHAVIOR OF APPLICATION

When the ONLINE application mismatch option is selected, a request for application transfer (%SW60.5) has to be done with a minimum delay of 2 seconds after any modification of the application.

Failure to follow these instructions can result in death, serious injury, or equipment damage.

System Bit %SW60.8

Swap Modbus on port 1:

%SW60.8 = 0

Address swap on Modbus port 1 when a switchover occurs.
%SW60.8 = 1

No address swap on Modbus port 1 when a switchover occurs.

System Bit %SW60.9

Swap Modbus on port 2:

%SW60.9 = 0

Address swap on Modbus port 2 when a switchover occurs.
%SW60.9 = 1

No address swap on Modbus port 2 when a switchover occurs.

System Bit %SW60.10

Swap Modbus on port 3:

%SW60.10 = 0

Address swap on Modbus port 3 when a switchover occurs.
%SW60.10 = 1

No address swap on Modbus port 3 when a switchover occurs.