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Debugging: Single Cycle Operation of the Safety PLC

To supplement the function test of the safety-related application, the Safety PLC provides the debug function "Single cycle operation". In single cycle operation, the Safety PLC interrupts the continuous cyclic processing.

Single cycles are only possible if the Safety PLC is in Debug Halt state. In single cycle operation, PLCnext Engineer displays a simulation in its online worksheets. No outputs are set on the Safety PLC or connected safety-related I/O devices. This means that the safety-related application does not function during single cycle operation.

WARNING
Unintended machine operation
  • Prior to executing single cycle operations in Debug Halt state, make certain that suitable organizational measures (according to applicable sector standards) have been taken to avoid hazardous situations as the safety-related application does not function.
  • Do not enter the zone of operation while executing single cycle operations in Debug Halt state.
  • Ensure that no other persons can access the zone of operation while executing single cycle operations in Debug Halt state.
  • Observe the regulations given by relevant sector standards while the machine is running in any other operating mode than "operational".
  • Use appropriate safety interlocks where personnel and/or equipment hazards exist.

To execute single cycle operations, proceed as follows:
  1. Activate the debug mode.
    The Safety PLC is now in Debug Run or Debug Stop state.
  2. Switch the Safety PLC to the Debug Halt state by clicking the Halt mode button in the Safety Cockpit or in any instance of a safety-related POU worksheet:

    The execution of the safety-related program is halted.

  3. To execute a single cycle, click the following icon on the Safety Cockpit toolbar or in any instance of a safety-related POU worksheet:

    The Safety PLC processes exactly one program cycle and then waits for the next command (which is either a further single cycle or exiting the Debug Halt state).

  4. To exit the Debug Halt state, click the Halt mode button again:

    The Safety PLC switches into the state from which Debug Halt was entered before.

Further Info
You can combine the single cycle operation with forcing/overwriting variables on the Safety PLC.