Virtual 3270 Interface › Control the Conversation › Panel Characteristics

Panel Characteristics

While any panel definition could be used for this conversation, the simpler the panel definition the easier it is for the interface user to process. Panel $USV3270 is used by both the Batch Command Interface and the TSO Command Interface and uses specific conventions.

The panel is defined as a Model-4 (43 line) panel, the first line containing three protected fields as follows:

• The first field contains the characters $USV3270 and can be used to verify that the interface user is connected to an NCL procedure designed to handle this type of communication.
• The second field contains the system variable &0. On output this will be substituted and contains the name of the currently executing procedure. This helps maintain synchronization throughout the conversation.
• The third field contains the system variable &RETCODE which can be used to determine the status of processing within the procedure.

The contents of these fields are extracted and placed into defined areas of the parameter list passed between the user program and the interface, regardless of whether the user requested all or only input fields be built in the Field Descriptor List. Hence there is an advantage in maintaining this first line convention for any application.

The second line of panel $USV3270 is an input field and contains the token name &REQUEST. This of course appears to the user program as the first input field in the Field Descriptor List and hence is easily accessible. Normally this would be used to describe the type of function that the interface user is requesting from the NCL procedure.

Subsequent lines of the panel are all input lines and may be used to contain qualifying input from the user application, or for returned text data from the NCL procedure.

Where any external application is required to use the services of the Virtual 3270 Interface, CA recommends that the procedures and panels described be used as models to assist development.