Cause of a Warm Restart

A warm restart may be caused:

  • by a power restoral without loss of context

  • by the system bit %S1 being set to 1 by the program

  • by Control Expert from the terminal

  • by pressing the RESET button of the power supply module of rack 0 (on Premium PLC)

Illustration

The diagram below describes how a warm restart operates.

Operation

The table below describes the program execution restart phases on warm restart.

Phase

Description

1

Program execution resumes starting from the element where the power outage occurred, without updating the outputs.

2

At the end of the restart cycle, the system carries out the following:

  • the initialization of message and event queues

  • the sending of configuration parameters to all discrete input/output and application-specific modules

  • the deactivation of the fast task and event processing (until the end of the master task cycle)

3

The system performs a restart cycle during which it:

  • re-acknowledges all the input modules

  • relaunches the master task with the bits %S1 (warm restart) set to 1

  • resets bit %S1 to 0 at the end of this first master task cycle

  • reactivates the fast task, the auxiliary tasks and event processing at the end of this first cycle of the master task

Processing a Warm Restart by Program

In the event of warm restart, if you want the application to be processed in a particular way, you must write the corresponding program conditional on the test that %S1 is set to 1 at the start of the master task program.

For Quantum PLCs, the switch on the front panel of the processor can be used to configure operating modes. For further details, see Quantum documentation.

Output Changes, for Premium and Atrium

As soon as a power outage is detected, the outputs are set in the fallback position:

  • either they are assigned the fallback value, or

  • the current value is maintained.

depending on the choice made in the configuration.

After power restoral, the outputs remain in the fallback position until they are updated by the task.

NOTE: after a power on while the CPU is not started, outputs are in security mode state (equal to 0). After the CPU start, if the module didn't stay powered on, the maintain state is lost and the output stay in state 0.

Output Changes, for Quantum

As soon as a power outage is detected:

  • the local outputs are set to zero

  • the outputs of the remote or distributed extension racks are set in the fallback position

After power restoral, the outputs remain in the fallback position until they are updated by the task.

Output Changes, for Extension Rack

If power outage occurs on rack where CPU is located:

  • Fallback state as soon as CPU loss is detected

  • Security state during I/O configuration

  • State calculated by CPU after the first run of the task driving this output

After power is restored, the outputs remain in the fallback position until they are updated by the task