# DIGITAL TCP/IP Services for OpenVMS
User's Guide

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You can determine the mode TELNET uses to transmit data. The appropriate TELNET mode for a session depends on:

- The remote host to which you are connecting
- The applications you use

Table 5-3 shows the modes that control TELNET communications.

Table 5-3 TELNET Transmission Modes
Mode | Function
--- | ---
Local Characters Mode | The local host interprets control characters, translating them into TELNET protocol sequences (ENABLE LOCAL_CHARS). Use this mode when the local and remote hosts implement different control characters. By default, characters are interpreted by the remote host (DISABLE LOCAL_CHARS).
Binary Mode | The local host sends transmissions in binary mode (ENABLE BINARY). Use this mode when the remote host expects each line of data to end with a carriage return/line feed combination. By default, the local host sends transmissions with the end-of-line character (EOL) mapped to the carriage return/line feed combination (DISABLE BINARY).
Debug Mode | TELNET displays data flow in both hexadecimal and readable text (ENABLE DEBUG). By default, TELNET displays data in readable text only (DISABLE DEBUG).
Character Transmission Mode | TELNET transmits data one character at a time (SET MODE CHAR) rather than line-by-line. Use this mode when you run a text editor (on the remote host) that does character processing. Character transmission mode is the default.
Line Transmission Mode | TELNET transmits data one line at a time (SET MODE LINE). Most clients send a character at a time. The remote host server must support line transmission mode. This allows you to do signal trapping as well as local character editing and tab expansion.

# 5.11 Sending Commands to the Connected Remote Host

While in input mode (an active session with a remote host), you can enter SEND commands that affect the remote host's processing of commands you have entered. You use these commands when the remote host does not recognize the default key or key sequence used for the same operation. You can use the SEND AYT and SEND NOP commands to determine if your session with the remote host is still open. Table 5-4 lists the functions available to you at the remote host with each SEND command.

Table 5-4 Sending Commands to the Remote Host
Function | Command | When to Use
--- | --- | ---
Abort output of the last remote command you entered, without discontinuing execution of the process. | SEND AO | You want to terminate output but not the execution of the process. After already aborting output, you want to resume output. The remote host does not recognize the Ctrl/O as the flush output character.
Determine if your connection with the remote host is still established, the remote host replying with connection status information. | SEND AYT | Test the connection to the remote host application and verify that the remote host application is responding. You are notified on success.
Terminate execution of the last command you entered at the remote host. | SEND BRK | The remote host does not recognize the Ctrl/C sequence as an interrupt character.
Delete the last character you typed at the remote host. | SEND EC | The remote host does not recognize your Delete key.
Delete the last line of text you entered at the remote host. | SEND EL | The remote host does not recognize your Delete key or command-line recall.
Signal the remote host that your local system is ready. | SEND GA | The application requires GA commands in either one or both directions.
Interrupt execution of the last command you entered at the remote host. | SEND IP | Your terminal or the remote host does not recognize the default interrupt character (Ctrl/C).
Determine whether your local host can send data to the connected remote host and whether the remote host can receive that data | SEND NOP | Check the communication path to the remote host; you are notified on error.
Interrupt the current process you are executing at the remote host, and in urgent mode (out-of-band), get a quicker response time to the interrupt. | SEND SYNCH | You want to clear immediately the communications path between your system and the remote host, with the remote host ignoring any incoming data not yet processed.

# 5.12 IBM 3270 Model Terminal Emulation (TN3270)

You can run a TELNET session with a host that uses IBM 3270 model terminals by using the TN3270 command. The TN3270 command:

- Provides IBM 3270 Information Display System (IDS) terminal emulation.
- Assigns IBM 3270 functions to your DIGITAL keyboard.
- Assigns IDS functions to specific keys.
  During a TN3270 session, you can:
  - Redefine keys interactively (Section 5.12.10.6).
  - Redefine keys permanently (Section 5.12.10.5).
  - Record your sessions (Section 5.12.6).
  - Troubleshoot problems (Section 5.12.11).

> Note

> When you run TN3270, you can only have one session. You cannot have other sessions running simultaneously, as you can when running normal TELNET sessions.

## 5.12.1 Supported IBM Terminal Models

Table 5-5 lists the IBM 3270 terminal models that TELNET/TN3270 can emulate.

Table 5-5 TELNET --- Supported IBM 3270 Model Terminals
Model | Screen Size (Rows x Columns)
--- | ---
IBM 3278 Model 2 | 24 x 80
IBM 3278 Model 3 | 32 x 80
IBM 3278 Model 4 | 43 x 80
IBM 3278 Model 5 | 27 x 132

## 5.12.2 Setting Up Your PC or Terminal for IBM 3270 Terminal Emulation

When you use TELNET and specify IBM 3270 model terminal emulation (TN3270), the image displayed on your screen depends on:

- The type of DIGITAL terminal you use, or that your PC is emulating.
- The features you set on it.

Sections 5.12.2.1 and 5.12.2.2 explain how to set up VT200- and VT100-series terminals (or emulation on PCs), respectively.

### 5.12.2.1 VT200-Series Terminal Setup

Follow these steps:

1. At the Set-up Directory menu, select the keyboard type that corresponds to the keyboard layout you are using (for example, North American).
2. At the Display Set-up menu, select the following:
   - Interpret controls
   - Light text, dark screen
   - Cursor (visible)
3. At the General Set-up menu, select the following:
   - VT200 or VT100 mode (if VT100 mode, set VT100 ID)
   - 7-bit or 8-bit controls
   - Multinational/national
   - Normal cursor keys
   - No new line
4. At the Communications Set-up menu, select the following:
   - XOFF at 64 or XOFF at 128
   - 8-bit communication line
   - 8-bit (any) parity
   - No local echo
5. At the Keyboard Set-up menu, select warning bell ON.

   At the DCL prompt, issue:

        $ SET TERMINAL /INQUIRE

   The software determines the terminal's characteristics and sets the appropriate parameters.

   If you select National Character mode, issue:

        $ SET TERMINAL /NOEIGHTBIT

   ### 5.12.2.2 VT100-Series Terminal Setup

   Follow these steps:

   1. Set your terminal to ANSI mode (see the user's guide for your terminal).
   2. Enter the following command at the DCL prompt:

          $ SET TERMINAL/INQUIRE

      This command causes the terminal to be questioned about its characteristics. The appropriate parameters for the terminal are set up according to its response.

   TN3270 requires DIGITAL terminals or DECterm windows that support at least 24 lines and 80 columns.

   ## 5.12.3 Starting and Exiting from TN3270

   Start a TN3270 session by using the TN3270 command. You can also use the TELNET/TERMINAL_TYPE=IBM-3278-n command. The default terminal type is IBM-3278-2. The following examples show several ways to start a TN3270 session, using the TN3270 command and connecting to host CENTRAL. For more information, see Section 5.3.

   - Using the default terminal type:

         $ TN3270 CENTRAL

   - Using a terminal type other than the default:

         $ TN3270/TERMINAL_TYPE=IBM-3278-4 CENTRAL

   You can invoke TN3270 and, without connecting to a remote host first, enter certain commands that customize the sessions and display parameters or status. You can also use a command file to invoke TN3270 and the customization.

   The TN3270 command includes several qualifiers that allow you to specify customized or special files for the following:

   - Character set translation tables file (/CHARACTER_SET=file) that translates between EBCDIC and the DIGITAL Multinational Character Set. The default file, if set up by your system manager, is SYS$LIBRARY:UCXTEDEF.TBL. If this file does not exist, and you do not specify a file, TN3270 uses its own translation table.
   - Keyboard definition file (/KEY_DEFINITIONS=file) that you create as an alternative to the default keyboard layout.
   - National Replacement Character Set (NRCS) file (/NATIONAL_CHARACTERS=n) for which your DIGITAL terminal is configured. The default for 8-bit terminals is MULTINATIONAL. The default for 7-bit terminals is US_ASCII.

   You can end a TN3270 session (close the connection) in one of the following ways:

   - At the remote host's system prompt, log out.
   - At the remote host's system prompt, return to the TN3270 prompt and disconnect the session, as follows:
     1. At the remote host's system prompt, press the TN3270 escape character (Ctrl/] is the default).
     2. At the TN3270 prompt, issue either DISCONNECT or close.

## 5.12.4 Getting Status

To monitor your TN3270 session, use the status line indicator at the bottom of your screen. A reverse-video strip displays status and information messages. To see status messages, issue the following:

    TELNET> ENABLE STATUS

## 5.12.5 Clearing Error Messages

TN3270 displays error messages in a bordered display at the bottom of your screen. This display overwrites the status display and remains visible until you clear it. To clear, invoke one of the following functions:

- REFR
- HELP
- SET FIL
- DEF KEY

## 5.12.6 Recording Sessions

During a TN3270 session, you can record your screen's contents. The PRINT function directs your screen's contents to either a file or a spooled printer.

To record your screen's contents, follow these steps:

1. Invoke the PRINT keyboard function, as explained in Section 5.12.9.
   The screen display is recorded in a file in a compressed state. Null lines (lines with only nulls and attribute characters) do not appear.
2. Invoke the ENTER function or any function that transmits the screen contents to the remote host's application, as explained in Section 5.12.9.

This creates the default output file, UCXTPRINT.LIS. TELNET does the following:

- Each time you start a TELNET session that runs TN3270, TELNET opens a new UCXTPRINT.LIS file.
- Each time you use PRINT during a session, TELNET appends new output from the screen to the end of UCXTPRINT.LIS.
- Each time you use PRINT, if you direct the output to a printer, TELNET creates a separate entry in the print queue.
- If the printer is spooled, TELNET immediately prints the output.

You can specify a different file name. To change the name, use one of the following two methods:

- When you start a TN3270 session, use the /PRINTER qualifier. Issue:

      $ TN3270 [ host ] /PRINTER=file

- During a TN3270 session, follow these steps:
  1. Use the SET FIL keyboard function, as explained in Section 5.12.9.
  2. At the prompt for a new file name, type a name.
     If you specify the same name that is already in use, subsequent PRINT operations direct output to a new version of the same file.
  3. Use the NEW LINE keyboard function, as explained in Section 5.12.9.

  ## 5.12.7 Online Help

  Online help during a TN3270 session displays:

  - A picture of the keypad
  - A list of TN3270 keyboard functions
  - The key combinations that invoke the TN3270 keyboard functions

  The Help screen shows the TN3270 functions as they correspond to the keys on your physical keyboard:

  - Top-row keys
  - Editing keypad
  - Application keypad
  - Up to 32 control or extended character definitions
  - All your definitions and changes, including those you make interactively

  To see the Help screen, use the HELP function which is key F15.

  ## 5.12.8 If the Keyboard Locks

  If your keyboard locks, the terminal bell rings, and the status line displays:

      Inhib

  To unlock the keyboard, press the following key to invoke the RESET function (KP0 refers to the 0 key in the application keypad on the righthand side of the keyboard):

      [KP0]

  Do not use the following functions when the cursor is in a protected field (a field that does not accept user input):

  - DELETE
  - DUP
  - ER EOF
  - FM
  - Any graphic character

  ## 5.12.9 Keyboard Functions

  This section describes the keyboard functions. Preceding each function description are the key sequences for VT100 and VT200 terminals and the function name to use in a DEFINE/KEY command. In many of the key sequences, TN3270 allows use of the extended function (EXT) feature. Used in conjunction with another key, EXT allows access to an extended function for that key. The extended function feature is described below in more detail.

  ATTACH

  VT100: EXT + E | VT200: EXT + Find
  DEFINE_KEY Function: ATTACH

  Changes control from one subprocess to another subprocess or to the parent process. When you invoke the ATTACH function, TN3270 uses the name of the last process to which you attached as the default process name.

  If you want to attach to a different process, press Ctrl/U to erase the default process name. You can then enter the process name of your choice at the prompt. The process name can be a quoted string. Use the quotation marks to preserve spaces, tabs, or lowercase letters in strings.

  ATTN

  VT100: EXT + A | VT200: F19
  DEFINE_KEY Function: ATTENTION

  Provides a way to "get the attention of" the remote application program that you are running by sending a SIGNAL RU command to the remote host. See the user's guide of the particular application program to learn what response the program gives when you use this key.

  Back Tab (| Left arrow)

  VT100: BACKSPACE | VT200: F12
  DEFINE_KEY Function: BACK_TAB

  Moves the cursor, depending on the type of screen. On a formatted screen, the cursor moves one of these ways, depending on the location when you press this key:

  - If the cursor is in a field, but not at the first position of the field, it moves to the beginning of the unprotected field that it is in.
  - If the cursor is in the first position of a field, it moves to the beginning of the preceding unprotected field. If the cursor is in the first position of the first unprotected field, the cursor moves to the first position of the last unprotected field on the screen.

  On an unformatted screen, the cursor returns to the first position on the screen.

  Cent Sign (¢)

  VT100: EXT + C | VT200: EXT + C
  DEFINE_KEY Function: (None)

  Enters a cent sign. If your terminal does not have this character, your screen displays a hyphen ( - ).

  CLEAR

  VT100: EXT + Enter | VT200: EXT + F20
  DEFINE_KEY Function: CLEAR

  Clears the screen and moves the cursor to the first position on the screen. When you invoke the CLEAR function, the software notifies the application program that this function has been used.

  DEF KEY (DEFINE key)

  VT100: Ctrl/K | VT200: Ctrl/K
  DEFINE_KEY Function: DEFINE_KEY

  Lets you interactively define or redefine a key. You get a prompt for the name of the key to define and for a function you want to assign to that key. Refer to Section 5.12.10 for more information about using the DEF KEY function.

  DELETE

  VT100: Delete | VT200: <X]
  DEFINE_KEY Function: DELETE

  Deletes the character at the cursor. The cursor remains where it is, and the other characters to the right of the cursor in the same field move one position to the left. The end of the field fills with blanks. Note that this is not the action normally associated with the Delete key on DIGITAL terminals.

  DSP ATT (display attributes)

  VT100: Ctrl/V | VT200: EXT + F17
  DEFINE_KEY Function: DISPLAY_ATTRIBUTES

  Enables and disables the visible attribute mode. This mode of operation forces display of the attribute characters (that is, the characters at the start of a field that indicate the display and data type of that field). In IBM 3270 model terminal emulation (TN3270), you can use the DSP ATT function to debug application programs, as explained in Section 5.12.12.

  DUP (duplicate)

  VT100: EXT + * | VT200: EXT + F12
  DEFINE_KEY Function: DUP

  Lets you enter a value in the same field in several forms without needing to repeat the entry for each form.

  After entering the data in the field on the first form, use the DUP function when at the same field on succeeding forms. The application program makes the necessary translation, filling in these fields with the same value. For details about the use of this key, refer to the user's guide of the particular application program.

  Displays an asterisk (*).

  DV CNCL (device cancel)

  VT100: EXT + U | VT200: EXT + Remove
  DEFINE_KEY Function: DVCNCL

  Cancels the RECORD function. Use the DV CNCL function if you begin using the RECORD function and then decide you want to stop. If you want to delete a sequence that has already been recorded on a PF key, use the RECORD function, press the PF key, and then use the DV CNCL function.

  ENTER

  VT100: Line Feed + Enter | VT200: Do + Enter
  DEFINE_KEY Function: ENTER

  Sends your input to the remote application program. While this communication is active, the keyboard locks and Inhib appears on the status line. Usually the application program releases the keyboard when it has finished processing your input.

  ER EOF (erase to the end of the field)

  VT100: EXT + KP, | VT200: F18
  DEFINE_KEY Function: ERASE_EOF

  Erases the contents of the current field, from the location of the cursor to the end of the field. The cursor remains in the same location.

  ER INP (erase input)

  VT100: EXT + KP- | VT200: EXT + F18
  DEFINE_KEY Function: ERASE_INPUT

  On a formatted screen, clears all the data in the unprotected fields on your screen and moves the cursor to the first position in the first unprotected field on the screen.

  On an unformatted screen, clears all the data and moves the cursor to the first position on the screen.

  You can also use the ER INP function to remove all previously recorded key sequences by using the RECORD function and then the ER INP function.

  EXIT

  VT100: Ctrl/Z or F10 | VT200: Ctrl/Z or F10
  DEFINE_KEY Function: EXIT

  Terminates the remote TELNET/TN3270 session. Aborts any exchange of data in progress between the local and remote hosts. Note that terminating a session with the IBM host in this way may result in improper termination of the session. For the appropriate logoff command string, see the user's guide for the IBM application with which you are communicating.

  EXT (extended function)

  VT100: KP. | VT200: KP.
  DEFINE_KEY Function: EXTEND

  Used in conjunction with another key, allows access to an extended function for that key. First invoke the EXT function and then press the second key. If you invoke EXT accidentally, invoking the RESET function cancels the EXT function.

  If the status display is enabled when you invoke the EXT function, the word Extend appears on the status line.

  FM (field mark)

  VT100: EXT + ; | VT200: EXT + F13
  DEFINE_KEY Function: FM

  Specifies the end of a field on an unformatted screen or the end of part of an unprotected field on a formatted screen. Refer to the user's guide of the remote application program for specific use of this key.

  Displays a semicolon ( ; ).

  HELP

  VT100: EXT + H | VT200: Help
  DEFINE_KEY Function: HELP

  Displays online help and an illustration of the TN3270 keyboard.

  HOME

  VT100: EXT + B | VT200: F13
  DEFINE_KEY Function: HOME

  Repositions the cursor to the first position in the first unprotected field on the screen (that is, to the beginning of the input area on the screen).

  Horizontal Control (Right arrow and Left arrow)

  VT100: Right arrow or Left arrow | VT200: Right arrow or Left arrow
  DEFINE_KEY Function: RIGHT, RIGHT_NOWRAP, LEFT, or LEFT_NOWRAP

  Moves the cursor horizontally across your screen without changing data you have already entered. If the cursor is at the:

  - End of a line when you use the Right arrow function, the cursor moves to the start of the next line.
  - Beginning of a line when you use the Left arrow function, the cursor moves to the end of the previous line.
    If the screen display you receive is wider than 80 columns, you can use the Right arrow and Left arrow functions to move through the display.
    If you want the cursor to wrap to the opposite edge of the display, use one of the following function sequences:
    EXT + Right arrow
    EXT + Left arrow

  INSERT

  VT100: EXT + PF4 | VT200: F14
  DEFINE_KEY Function: INSERT_MODE

  Enables insert mode. Use insert mode to edit what you typed. If the status display is enabled, Insert appears.

  In insert mode, when you type a character into an unprotected field, it is displayed to the left of the cursor, moving the following one position to the right:

  - The cursor
  - The character at the cursor location
  - All the characters to the right of the cursor in the field

  You can insert characters into an:

  - Unformatted screen
  - Unprotected field on a formatted screen until it is full

  If you attempt to insert characters after the field is full, the keyboard locks, the terminal bell rings, and the word Inhib appears on the status line. If the keyboard locks when you try to insert characters into a field that looks empty, the field might have trailing spaces. To erase these spaces, use the ER EOF function.

  To return your screen to the normal mode of entry, use one of the following keyboard functions:

  - RESET
  - CLEAR
  - ENTER
  - Any PA key
  - Any PF key

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