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This chapter introduces 5250 emulation and describes the features provided by the SNAP-IX 5250 emulation program.
This section provides the background to the 5250 support provided by the SNAP-IX 5250 emulation program and describes:
The 5250 Information Display System (IDS), and the SNAP-IX 5250 emulation program's support for it
The two types of sessions that the 5250 IDS uses to communicate with application programs on the AS/400
The 5250 screen that display applications on the AS/400 use to present data and collect new information
The 5250 IDS is a family of display stations and printers that was originally designed to support data entry and inquiry applications running on the AS/400. The 5250 IDS uses sessions to communicate with application programs on the AS/400.
The SNAP-IX 5250 emulation program provides you with access to most of the standard features of an IBM 5250 IDS terminal and printer so that you can run existing 5250 applications unchanged. In addition, the 5250 emulation program provides a session control interface, local copy, and macro record and replay capabilities.
The 5250 application programs on the AS/400 use 5250 sessions to communicate with the local computer. There are two types of AS/400 application programs: display applications and printer applications. Each type of program uses its own type of session to communicate with the SNAP-IX computer.
The AS/400 display applications use display sessions to show a 5250 formatted screen that you can use to interact with the application. The SNAP-IX 5250 emulation program displays this screen in a session window. Display sessions implement the 5250 datastream standard that was originally used by a group of IBM hardware products including display stations (such as the 5251, 3477, and 5555) and control units (such as the 5294). The 5250 screen is described in 5250 Formatted Screen.
The AS/400 printer applications use printer sessions to communicate with SNA Character String (SCS)-capable printers and print information from the AS/400 locally. You cannot interact directly with AS/400 printer applications because there is no screen or session window associated with a printer session. The SNAP-IX 5250 emulation program implements the SCS datastream standard that was originally used by a group of IBM hardware products including printers (such as the 3812, 5256, and 5224).
The SNAP-IX 5250 emulation program supports multiple 5250 sessions concurrently between the SNAP-IX computer and one or more AS/400s. Therefore, you can communicate with many different AS/400 application programs from one computer. The number of sessions that can be supported is limited only by the resources that are available to SNAP-IX.
The AS/400 display applications use a 5250 formatted screen to interact with users. Each location on the 5250 formatted screen can be addressed separately. Instead of having text that scrolls off the top of the screen as you type in new information, the 5250 screen can be divided into different areas, called fields.
A field is an area of the 5250 screen. Each field can be given its own
characteristics (or attributes), and can be updated individually. AS/400 display applications
typically present you with a screen of information organized under headings.
Headings are fields that are protected
so that the user cannot
write information into them. Organizing the data into fields in this way makes
it easier to read and update information about the AS/400. In addition to
this, the 5250 screen is designed to provide the following benefits:
When a field is updated, only that one area of the screen needs to be changed instead of redrawing the whole screen.
Only the data in data fields is sent to the AS/400 instead of sending information about the whole screen.
The terminal can do part of the data validation before it
sends the data on to the AS/400 (such as the size of
the data).
The 5250 screen uses an invisible attribute character at the beginning
of each field to determine the behavior of the field. For instance, it can determine whether you
can enter data in the field (whether the field is protected
or not) and, if so, the type of data you can enter-for example, numeric
or alphanumeric. The attribute character also determines whether information
is displayed and, if it is, determines the intensity or color of the display.
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