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3270 Host Connection Program 2.1 and 1.3.3 for AIX: Guide and Reference

Programming HLLAPI

The High-Level Language Application Programming Interface (HLLAPI) is an application programming interface (API) supported by the AIX 3270 Host Connection Program (HCON). This interface enables a program on a workstation to access a host presentation space. A host presentation space is a region in computer memory that can be displayed on the screen of a 3270 terminal emulator.

Consult the following for more information about HLLAPI:

HLLAPI for AIX 3270 Host Connection

The High-Level Language Application Programming Interface is an API supported by HCON. This interface allows workstations to interact with a host using 3270 terminal emulation. Consult the following for more information about the High-Level Language Application Programming Interface:

HLLAPI Execution Environment

The HLLAPI application executes in a process environment. When you run the HLLAPI application, the following processes are generated:

Name Description
hcondmn Daemon process
e789x Emulator child process for each session as initiated by the HLLAPI program
e789lus Emulator child process for DFT SNA protocol processing
fxfer File File transfer parent process
dfxfer File File transfer child process

The HLLAPI Execution Environment figure illustrates HLLAPI processes.

Note: The xhconx process may be used in place of the e789x process if xhcon is started explicitly.

HLLAPI Components

The HLLAPI components of HCON provide comprehensive communications capabilities in a single system. HCON enables users to connect directly or indirectly (using control unit) to a range of workstations.

The following figure represents the components of the AIX Host Connection Program (HCON).

Uses of HLLAPI

HLLAPI is a valuable tool in a variety of work environments. It provides interaction between mainframes and workstations, thereby enabling both inexperienced and experienced users to become more productive.

HLLAPI acts as a programmed operator (a program that performs and monitors activities that are usually done by the user). HLLAPI can perform the following functions:

In addition, HLLAPI facilitates communication from workstation application programs to host application programs by using the 3270 data stream structured fields. This allows for the generation of programs, such as the file transfer applications used to transfer files between host and workstation environments.

HLLAPI Services

HLLAPI is divided into several service groups:

HLLAPI Connections

HLLAPI supports the following 3270 connections:

HLLAPI Presentation Spaces

A Presentation Space (PS) is a region in computer memory that can be displayed on the screen of 3270 terminal emulation. Mainframe interactive (MFI) or host sessions are 3270 sessions that are displayed on the screen of a 3270 terminal emulation. These sessions keep data transmitted to and from a host application.

Each PS has a unique one-character identifier called a short name. The short name is defined in the session profile of a user.

Some host programs can override the configured size. Host override size is typically 1920 bytes. The host override is always less than the configured PS size for 3270 terminal emulation sessions.

HLLAPI functions use the PS size as defined by the host program. The supported sizes are:

Printer Sessions

An application can connect only to host PS. There are two types of host sessions: display and printer. The printer session contains a PS but it cannot be connected to by an application.

Printer sessions are supported only by QUERY SESSIONS (10) and QUERY SESSION STATUS (22).

Running HLLAPI Programs

There are no special steps to execute your HLLAPI program. Refer to "Programming with HLLAPI" for more information.

HLLAPI Current Connection

To communicate with a host session, an application must be connected using the CONNECT PRESENTATION SPACE (1) function. This function allows the sending or monitoring of host presentation space activity.

The term "current connection" refers to the most recent connection between the HLLAPI application program and the specified host PS using the CONNECT PRESENTATION SPACE (1) function. For example, if the HLLAPI application connects to PS short name A, and then connects to PS short name B, PS short name B becomes the current connection. Any further PS functions are sent to PS B, the current connection. The application must connect to A to make it the current session before sending any functions to that PS.

Keyboard Remap with Utility Session

The AIX 3270 Host Connection Program keyboard remap has no effect on HLLAPI functions that send data to the host PS.

Ending HLLAPI Communication

The following is required to disconnect your HLLAPI application:

  1. Stop all keystroke intercept sessions by issuing the STOP KEYSTROKE INTERCEPT (53) function to all PSs for which the START KEYSTROKE INTERCEPT (50) function was issued.
  2. Disconnect each connected PS from each thread that performed a CONNECT PRESENTATION SPACE (1) function. Disconnection is accomplished by using the DISCONNECT PRESENTATION SPACE (2) function. This affects only the current connection; therefore, it is necessary to reconnect to a presentation space before disconnecting it.
  3. Stop all HOST NOTIFICATION for all sessions by issuing the STOP HOST NOTIFICATION (25) to all sessions that have an active START HOST NOTIFICATION (23) function.
    Note: Your HLLAPI application can use the RESET SYSTEM (21) function to disconnect all PSs. If the display session is terminated by pressing the Ctrl-D key sequence twice, or if the session process is stopped, your HLLAPI program must be stopped. Then, both the display session and your HLLAPI program can be restarted.

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