Different block types are used in Control Expert. The general term for all block types is FFB.

Elementary functions (EF) have no internal status and one output only. If the input values are the same, the value at the output is the same for all executions of the function, e.g. the addition of two values gives the same result at every execution.

Elementary function blocks (EFB) have an internal status. If the inputs have the same values, the value on the outputs can have another value during the individual executions. For example, with a counter, the value on the output is incremented.

Derived function blocks (DFBs) have the same properties as elementary function blocks. They are created by the user in the programming languages LD, FBD, IL and/or ST.

Procedures are functions with several outputs. They have no internal state.

The only difference from elementary functions is that procedures can have more than one output and they support variables of the VAR_IN_OUT data type.

Procedures do not return a value.

Procedures are a supplement to IEC 61131-3 and must be enabled explicitly.

There is no visual difference between procedures and elementary functions.