Description

In this operating mode, input acquisition, the processing of the application program and the updating of outputs are all carried out periodically over a defined period of 1 to 255 ms.

At the start of the PLC cycle, a time out whose current value is initialized to the defined period starts the countdown.

The PLC cycle must be completed before this time out expires and launches a new cycle.

Operation

The following diagram shows the execution phases of the PLC cycle.

%I Reading of inputs

%Q Writing of outputs

Operating Mode

The processor carries out internal processing, input acquisition, processing of the application program and the updating of outputs in that order.

  • If the period is not yet over, the processor completes its operating cycle until the end of the period by performing internal processing.

  • If the operating time is longer than that assigned to the period, the PLC signals a period overrun by setting the system bit %S19 of the task to 1. Processing then continues and is executed fully (however, it must not exceed the watchdog time limit). The following cycle is started after the outputs have been implicitly written for the current cycle.

Cycle Check

Two checks are carried out: