2.2 The IBM 7171 ASCII Device Attachment Control Unit - Index of

Chapter 3. Using ASCII Terminals on the IBM 7171This chapter is for ASCII terminal users. It explains how the IBM 7171 emulates3270 terminal functions for ASCII display terminals. It assumes that the user isfamiliar with the functions of a 3270 terminal. If this is not the case, the full complementof IBM 3270 Information Display System products is identified in theintroductory publication An Introduction to the IBM 3270 Information DisplaySystem, GA27-2739. For more detailed 3270 information refer to the IBM 3270Information Display System Data Stream Programmer's Reference, GA23-00S9.3.1 IBM 3270 Emulated and Extended FunctionsThe IBM 7171 not only emulates a 3270 terminal for its attached ASCII terminals,in some .cases it extends these functions to make interactive text and programediting more effective.I 3.1.1 3270 Alternate Screen Size Support3270 Alternate Screen Size Support has been added. The IBM 7171 now requiresscreen size information for both the logical screen sizes (the 3278 model supported)and the physical screen sizes (the sizes the ASCII terminal is capable ofsupporting). If the terminal physical size is too small to view the entire logical3270 size, there are two new input sequences defined to "Page Up" and "PageDown." Thus, an ASCII display that only supports a 24x80 screen can be definedto support a 3278 Model Group 4 (which has a 43x80 screen) and it can view theentire 43x80 logical screen by scrolling the 24x80 physical screen. The 3278Model Group S can also be supported by an ASCII device, as long as that device iscapable of displaying 132 columns of output, such as the DEC VT100. In the caseof the VT100, which can display a 24x132 screen, the Page Up and Page Downfunctions can be used to display the missing lines that a 27x132 3278 ModelSwould display.3.1.2 Different Character RepresentationThere are two important EBCDIC characters which are not defined in ASCII andtherefore usually cannot be found on the keyboard of an ASCII terminal:- the "cent" symbol (¢) and- the "not" symbol (....,)Since these symbols can be important in certain programming languages andeditors, the IBM 7171 represents them with two less important ASCII characters:Chapter 3. Using ASCII Terminals on the ffiM 7171 3-1