CSPG - page retrieval

Some transactions, especially those performed on screens, produce a response that is too large to be displayed or printed at one time. The whole response is held on direct access storage, and only the first portion (called a page) is displayed. You can manipulate these pages, through basic mapping support (BMS), using the CSPG page retrieval transaction. You can use paging to view all pages of the response, in any order. All the pages produced by a transaction make up a logical message.

A page retrieval session begins when you enter the first page retrieval command, or when the first page is presented by automatic transaction initiation (ATI). During the session, CICS® passes commands directly to BMS terminal paging, without following the normal transaction identification procedure.

When using BMS for IBM® 3780 Communication Terminal transactions, switch off the SPACE COMPRESS EXPAND (standard feature), TRNSPCY (special feature), and the INHIBIT IRS (special feature) switches.

Pages to be manipulated with paging commands must have been created by BMS, which must be active in the system to service the commands. Paging commands enable you to:
  • Retrieve a page.
  • Display information about logical messages queued for your terminal.
  • Chain a logical message, that is, retain the previous logical message on direct access storage while you enter a new transaction.
  • Purge a logical message, that is, erase it from direct access storage; a paging session must be ended by purging the message.
  • Copy a page to another terminal.

You select the above functions by entering a unique identification code for each function. This code is 1 – 7 characters long, and is defined by the PGRET, PGCHAIN, PGPURGE, and PGCOPY system initialization parameters.

Note: Do not use codes that are the same as the leading characters of any transaction defined to CICS by a TRANSACTION resource definition.

Single keystroke retrieval (SKR)

If you use a 3270 display device under z/OS® Communications Server, you can use PA or PF keys, as defined in the SKRxxxx system initialization parameter, to enter page retrieval commands, and greatly reduce the number of keystrokes necessary in a page retrieval session. After the session has ended, the PA and PF keys can again be used for initiating transactions in the usual way. The SKRxxxx system initialization parameter gives further information about this topic.

Page retrieval for logical devices

Your application program can send messages to a communication system such as the IBM 3600. Your application program can also send different pages to each of the logical devices within the system. These pages must be grouped as a single logical message, held in storage.

Each part of a logical message is accompanied by a logical device code (LDC) that identifies its destination. When retrieving the pages for a logical device, you must specify the LDC for that device. However, you do not need to do this if the user-written program in the logical device controller provides a default LDC mnemonic.

If you specify the page number and *ldc, delivery begins with the specified page for that logical device. If the logical device is in AUTOPAGE status, all pages for that logical device, starting with the requested page, are written. If the logical device is in PAGE status, only the specified page is written.

If you omit *ldc, and the application program in the logical device does not provide a default, BMS selects the first page destined for a logical device that is currently in PAGE status. The application program in the logical unit should provide a default LDC, because pages may be delivered to logical devices other than those you originally specified.

In either case, if your request is the first request for a page from a logical message, all pages (within the logical message) destined for logical devices currently in AUTOPAGE status are delivered after the first or specified page is delivered to a device in PAGE status.

The getpageA command supports an *ldc specification for non-routed messages created for a 3601 logical unit. The various forms of getpageA are interpreted as follows:
  • getpageA*ALL resets to autopaging and delivers all pages for the logical devices that have autopage specified in the terminal definition, but that were temporarily placed in page status by the CICS application programmer.
  • getpageA*ldc resets the specified logical device to autopage and delivers the pages for that *ldc. The command is similar to getpageA*ALL, except that it operates only for the specified logical device.
  • getpageA resets to autopaging and delivers the remaining pages for the logical device for which pages are currently being displayed.

Page retrieval and partitions

The page retrieval commands, including any PA and PF keys used in single keystroke retrieval, refer to the partition in which they are entered. The partition in which the last paging command is entered is the current partition. A paging command for a partitioned message entered on a nonpartitioned screen (that is, after CLEAR) refers to the current partition.

After a transition from base (unpartitioned) state to partitioned state, or a change of partition set (that is, the initial page display, a page display following CLEAR, or following a change in the level of page chaining), the current page is displayed in each partition. The current page is initially the first page for that partition. It is updated by page retrieval commands.