A VA Smalltalk program needs to be aware of the details of the host application to which it will be communicating. It needs to know the flow of control from screen to screen in order to access the desired data. It must also handle exceptional cases, such as a communication line failure or a control-unit problem. This functionality resides in the basic level of the VA Smalltalk / VAST Platform underneath the level that supplies support for VA Smalltalk parts...

You need to create and connect an (Abt3270Terminal) object to a live terminal-emulator session; this means the Communications Manager for the workstation must be running. After the connection is established, the terminal session can be placed under programmed control by sending messages to the (Abt3270Terminal) object.

Two procedures exist for retrieving data from the screen. The first choice is to use methods like stringAt:for:, which retrieves the string starting at a given point for a given length. The second choice is to use the buildFieldDefsOfType: method to create a record from the screen. This can then be used with at: to read data from the screen.