At a Glance

The communication functions used with Premium and Atrium PLCs have certain unique characteristics which set them apart from the other functions of the library. This documentation complies with the documentation charter concerning the function library, but also contains additional information relating to the particularities of the communication specific-application.

Located Variables

All communication functions that do not require programming in the server PLC (READ_VAR, WRITE_VAR, etc.) provide access to the located variables of remote PLCs. Unlocated variables are not accessible.

NOTE: To perform inter-PLC transfers of unlocated variables, it is necessary to use the DATA_EXCH function. Another solution is to make local copies in the located variable zones.

Apart from the first example of the WRITE_VAR function (only Control Expert M and higher), all of the other examples are made using direct addressing variables (use of addresses, located variables).

Programming Language

The most concise programming language for creating communication applications is Structured Text language (ST). All of the examples, except that of the READ_VAR function, are therefore written in ST.