Instance Data Blocks

The concept of the instance data blocks is explained in detail in the section function blocks. In the data memory these are completely normal data blocks whose data you can access in the usual way.Usually this is not done. In the CPU there is another register (in the picture DI-No) in which the number of the currently opened instance data block is saved. If you want to access data of this block you will have to use the following notation:

      DIX 7.2     bit no. 2 of byte 7 of the DB with the number in DI- register

      DIB 9       byte 9                 ´´

      DIW 10      word 10                ´´

      DID 16      double word 16         ´´

This is just one possibility to access data, usually data out of instance data blocks are addressed by the name that is specified in the declaration part of the accompanying FB.

See also:

PLC

Data Memory

Naming the In- and Outputs as well as the Marker

Naming the Data in Data Blocks