General

Event processing take priority over tasks.

The following illustration describes the 3 defined levels of priority:

Management of Priorities

• EVT0 event processing is the highest priority processing. It can itself interrupt other types of event processing.

• EVTi event processing triggered by input/output modules (priority 1) take priority over TIMERi event processing triggered by timers (priority 2).

• On Modicon M580, M340, Premium and Atrium PLCs: types of event processing with priority level 1 are stored and processed in order.

• On Quantum PLC: the priority of priority 1 processing types is determined:

  • by the position of the input/output module in the rack,

  • by the position of the channel in the module.

  The module with the lowest position number has the highest level of priority.

• Event processing triggered by timer is given priority level 2. The processing priority is determined by the lowest timer number.

Control

The application program can globally validate or inhibit the various types of event processing by using the system bit %S38. If one or more events occur while they are inhibited, the associated processing is lost.

Two elementary functions of the language, MASKEVT() and UNMASKEVT(), used in the application program can also be used to mask or unmask event processing.

If one or more events occur while they are masked, they are stored by the system and the associated processing is carried out after unmasking.