General Points

Discrete modules have different associated IODDTs.

The IODDTs are predefined by the manufacturer. They contain input/output languages objects belonging to a channel of a specific application module.

There are 4 IODDT types for the discrete modules:

  • T_DIS_IN_GEN

  • T_DIS_IN_STD

  • T_DIS_OUT_GEN

  • T_DIS_OUT_STD

NOTE: IODDT variables may be created in two ways:

Language Object Types

Each IODDT contains a group of language objects which are used to control them and check their operation.

There are two types of language objects:

  • Implicit Exchange Objects, which are automatically exchanged at each cycle pass of the task associated to the module

  • Explicit Exchange Objects, which are exchanged upon demand from the application, while using explicit exchange instructions

Implicit exchanges concern the module inputs/outputs: measurement, information, and operation results.

Explicit exchanges enable module configuration and diagnosis.

NOTE: In order to avoid several simultaneous explicit exchanges for the same channel, it is necessary to test the value of the word EXCH_STS of the IODDT associated to the channel before to call EF using this channel.