CHAPTER
&.
SERVICE INVOCATIONThe CICS/VS system management com~onent provides the following supervisory and data management services:
• Terminal services - Terminal Management/Terminal Control program
• Fil~ services - File Management/File Contrel ~rogram
TERMINAL
• Transient data services - Transient Data Management/Transient Data Control program
• Temporary storage services - Temporary Storage Management/Temporary Storage Control program
• Storage services - Storage Management/Storage Control program
• Program services - Program Management/Program Control program
• Time services - Time Management/Interval Control program
• Task services - Task Management/Task Control program
• Journal services - Journal Management/Journal Control program
• Restart/recovery services - sync Point Management/Sync Point program Each program performs the following basic steps:
1. Analyzes a specific service request issued by an application program or another CICS/VS program
2. Performs the requested service by communicating with the operating system, as necessary, through macro instructions 3. Retains the status of each service request until the service is
provided
4. Maintains statistical information that can be used to evalulate system performance
This chapter, building
On
the introduction of Chapter 1, explains these services and how the applicaticn programmer uses macroinstructions to request them. When preparing programs for CICS/VS, however, the programmer should refer to the discussions of specific macro instru.ctions in Chapte r 7.
TERMINAL S ERVI CES
Terminal management provides for communication between terminals and user-written applica ticn ~rograms through terminal control.
Terminal control is responsible for the polling and addressing of terminals, code translation, transaction initiation, task and line synchronization, and the line control necessary to read from or write to a terminal. The user-written application program is thus relieved, as much as possible, from having to control the physical terminal environment.
Requests for terminal services are communicated directly to terminal control through CICS/vS macro instructions. Individual application
Chapter 6. Service Invocation 59
programs thus interface with a terminal both logically and symbolically.
Before issuing a DFHTC macro instruction, the application programmer must make sure that TCAFCAAA contains a terminal centrol table terminal entry (TCTTE).
Terminal control operates as a system-provided task, under control of its own TCA. It contends for system resources .ith user-provided tasks in the system, but i t is the highest-priority task in CICS/vS.
Terminal control is always the first task to be dispatched by CICS/VS;
it scans the service request indicators in theTCT and performs requested services.
In providing for communication between user terminals and
user-written application programs, CICS/VS uses standard access methods available with the host c~erating system (DOS/VS or OS/VS). The Basic Telecommunications Access Method (PrAM) ,is used by CICS/VS for terminal management of most start-sto~ and BSC terminals. As an option for OS/VS, the Telecommunications Access Method (TCAM) can be specified.
The Sequential Access Method (SAM) is used where key-driven terminals are simulated by sequentia I devices such as ca'rd readers and line printers. The Virtual Telecommunications Access Method (VTAM) is used for terminal management of system network architecture (SNA) terminal systems.
Note: The last data character in each logical in~ut record from a sequential device must be followed immediately by a character defined as an end-of-block (EOB) character by the system ~rogrammer. For sequential devices, the last entry in the input stream should be CSSF
(control system sign-of,f) GOODNIGHT or CSOT RECV to provide a logica I close. If end of data (EOD) is encountered, all subsequent reads are treated as errors and only writes are processed. There may be multiple logical records on a single ~hysical record (multiple EOD characters on a single card). For users of CICS/OS/VS having blocked SYSIN or SYSOUT, overriding DD statements rrust be ~rovided to specify unblocked for CICS/VS data sets used to sirrulate terminals.
The terminal management macro instruction (DFHTC) is used to request any of a wide variety of services. Among them are same services of interest to users at terminals of most, if not all, terminal types supported by CICS/VS. These include:
• Write data to a terminal
• Read data from a terminal
• Synchronize terminal input/output for a transaction
• Converse with a terminal
• Read or write multiple records to a card reader, disk data set, magnetic tape unit, or line ~rinter defined by the system programmer as a card-reader-in-line-printer-out (CRLP) terminal.
For additional informatio~ concerning the last of these services, see "sequential Terminal Sup~ort" in Chapter 8.
Other services performed in res~onse to DFHTC macro instructions are applicable to specific terminal types. Since many types of
terminals are supported by CICS/VS, many special services are provided.
(FOr a list of terminals sup~orted by CICS/vS, see the CICS/VS General Information Manual.) The list below is representative of the
terminal-oriented input/output services available:
• Read the entire contents of a buffer (3270 Information Display System)