An instance of this type encapsulates an editable text area. The number of rows and columns displayed in the text area is given by the SIZE input, and its initial contents are given by the IVAL input. Upon the occurrence of a REQ+ input, the string present at the IN input is appended to the contents of the text area and a CNF+ output is issued. If a REQ- event occurs, or the text area is not initialized, the text is not appended and a CNF- output is issued.

The operation of an instance of this FB type is modeled by the service sequences shown below.

See the MONITOR device configuration for an example of the use of an instance of this type.