Chapter 5

VT100 Family of Video Terminals

Overview

Digital’s VT100 video terminal, introduced in 1978, has set industry standards for functionality and reliability. The success of the VT100 led to the development of a “family” of video terminals – the VT101, the VT102, the VT125, and the VT131. Each of these terminals offers all the features found in your VT100.

VT100, VT101, VT102, VT125, and VT131, terminals can be used with any of Digital’s processors – PDP-8s, MICRO/PDP-11s, PDP-11s, VAXes, DECsystem-10s, and DECSYSTEM-20s. These video terminals can work with other vendor’s systems as well as with Digital systems. Because half-duplex communications and ASCII support are features of the VT102 and VT131 video terminals, they have the capability to work with more systems.

Models

The VT100 offers the following models:

VT100-AA

CRT with EIA interface, universal power supply, 120 Vac plug

VT100-AB

CRT with EIA interface, universal power supply, 240 Vac plug

VT100-WA

VT100-AA, including advanced video option and word processing keyboard

VT100-WB

VT100-AB, including advanced video option and word processing keyboard

VT100-WC

VT100-WA with French Canadian word processing keyboard

VT100-WD

VT100-WB with French Canadian word processing keyboard

VT100-WE

VT100-WA with French word processing keyboard

VT100-WF

VT100-WB with French word processing keyboard

VT100-WG

VT100-WA with Dutch word processing keyboard

VT100-WH

VT100-WB with Dutch word processing keyboard

VT100-WJ

VT100-WA with German word processing keyboard

VT100-WK

VT100-WB with German word processing keyboard

Major Features

No matter which Digital video terminal you select, the VT100, VT101, VT102, VT131, or the VT125, each member of the VT100 family contains the following universal features.

User-Oriented Features

Detached sculptured keyboard

The keyboard and monitor can be positioned separately for optimum use in your work environment. Since the keyboard has a layout similar to that of an office typewriter, the transition from office typewriter to terminal is easy.

ASCII character set

Industry standard ASCII characters offer compatibility with Digital and non-Digital systems.

Numeric/application keypad

The calculator-style numeric keypad ensures fast and easy number entering in data entry and financial applications. The application keypad transmits control sequences instead of numeric codes that act as program function codes to control predefined application-specific routines.

Cursor control keys

These send codes to the host to let you easily and quickly position the cursor anywhere on the screen with a minimum of keystrokes.

Keyboard-selectable features

These include communication speeds, keyclick, margin bell, dark/light background, and block/underline cursor. You can configure the terminal to your personal preferences to maximize your productivity.

Non-volatile memory set-up

Allows you to save and later recall the keyboard features you have selected.

80 column × 24 lines display format

Used for standard video terminal applications.

132 column × 14 lines (VT100, VT101, VT125) display

Allows you a larger format for detailed or spread sheet work so you can preview reports prior to printing. (Note: The advanced video option, which is standard with the VT102 and VT131, provides 132 column × 24 lines display.)

Selectable bidirectional smooth screen scrolling

With this feature you can select smooth scroll or jump scroll. The smooth scroll feature of the VT100 family, when used with XON/XOFF transmission control, lets you read new lines of text easily, even when transmission speeds are high. When jump scroll is selected, new lines appear on the screen as fast as the host sends them to the terminal. At higher baud rates, data can be difficult to read due to the rapid movement of lines.

Split-screen capability

With this feature, the host can scroll any subset of the 24-line screen, while the rest of the screen remains fixed. This feature is useful for many applications. For example, the host can maintain status information on a fixed portion of the screen while interactive work is performed in the scrolling area. This permits you to work with two information sources.

Double-width/double-height characters on a line-by-line basis

This feature can provide versatility in display format for forms, prompting, and text applications.

Reverse video

This is another selectable feature that allows you to change the screen from black characters/white background to white characters/black background, according to your preference.

Selectable screen intensity

You can adjust the screen to the amount of light in the room for easier reading, and to suit personal preferences.

Engineering Features

ANSI-compatible command set

Terminal commands are compatible with ANSI 3.64 standards.

VT52-compatible command set

Permits compatibility with VT52 software.

Line drawing character set

The basic character set features 32 line drawing and other graphic characters. These can be used to present solid-line displays of simple forms and data plotting in a format that looks like that of a hardcopy printout. (See Appendix A for more information on the VT100 line drawing character sets.)

20-character answerback message

Provides you terminal with the ability to identify itself by sending a message to the host. This message may be sent by the operator or automatically sent to the host without operator intervention.

EIA RS-232 serial line interface

The VT100 family interfaces to asynchronous communications line with a 25-pin connector, mounted on the back of the terminal. This meets the requirements of EIA specification RS-232-C, the industry’s standard.

Full-duplex communication

Enables two-way simultaneous transmission between your terminal and the host.

Automatic XON/XOFF buffer control

Generates synchronizing codes XOFF/XON that can stop or resume data transmission.

Keyboard-selectable baud rate to 19,200 baud

Achieves compatibility in communications between the video terminal and the host or between the video terminal and another device, such as a printer.

Easy Serviceability

Self-test diagnostics

These diagnostics automatically or on command test the condition of the terminal’s non-volatile and internal memory, keyboard, and advanced video memory (if this option is installed) to determine if a fault is present.

Modular design

Ensures easy, fast, and inexpensive maintenance.

Screen Attributes

Digital’s VT100 family of terminals allows a standard screen display of 24 lines by 80 characters. Individual characters are based on a 7-by-9 dot matrix format for crisp, clear display.

Options

The following options are available for the VT100 terminal.

Accessories and Supplies

The following VT100 family accessories, supplies, components, and spares are available for the VT100, VT101, VT102, VT131, and VT125 video terminals. Check with your sales representative or Digital’s Installed Base Group for the latest information. Note: While many of these products are for sale in European and GIA countries, some items may not conform to national standards. Again, it is recommended that you consult your local Digital dealer/distributor for details.

Accessories

Spares

Hardware Aids

Tools

Controls and Indicators

VT100 family terminals perform two functions. First, they act as an input device to the computer, by sending the information you enter through the keyboard to the computer. Second, they simultaneously act as an output device for the computer, displaying data on the video screen. The controls and indicators described below are found on the VT100, VT101, VT102, VT131, and VT125 terminals.

Keyboard Controls

Keyboard Indicators

Seven indicators are located on the VT100, VT101, VT102, VT131, and VT125 keyboards.

The On-Line indicator lights to show that the terminal is on-line and ready to transmit or receive messages. The Local indicator lights to show that your terminal is off-line and cannot communicate with the host. In local mode, the keyboard remains active and all characters typed appear on the screen, but are not transmitted to the host.

The Keyboard Locked indicator shows that the terminal’s transmit input buffer is full, and the keyboard cannot be used to enter data. Even when the keyboard is off, the terminal can still receive data from the host. Once the data is transmitted, and the buffer empties, keyboard transmission resumes.

LED Indicators – L1, L2, L3, and L4 – found on the VT100, VT101, and VT125 terminals, are customer-programmable and can be assigned any meaning for specific applications. The User Guide for your specific terminal will have details on the escape sequences necessary to program these LEDs. The VT102 and VT131 terminals have dedicated LEDs. See Chapter 6 or your User Guide for more details.

Monitor Controls and Indicators

VT100 family monitors have only two controls: the power switch and the power selector switch, which is used to adapt the terminal to the available ac input voltage range.

In addition, there are three audible alarms associated with the VT100 family of terminals.

A keyclick is sounded by the terminal whenever a key is pressed. The following are exceptions:

• Shift or CTRL keys do not generate a keyclick because these keys do not transmit a code to the host, but merely modify the codes transmitted by other keys.
• KBD LOCKED indicator is turned on. In this case, the characters typed are lost.
• The keyclick feature was turned off in Set-Up mode.

The long tone (bell) is sounded by your terminal to indicate one of the following:

• A bell code was received from the host.
• The cursor is eight characters away from the right margin and the margin bell is enabled.

Finally, your terminal will sound the long tone several times in rapid succession to indicate that the nonvolatile memory had difficulty in reading or writing the set-up features. If this occurs, check the set-up features and then perform a recall or save operation.

Operator Features

All VT100 family members incorporate features that can be selected in set-up. Set-up features reflect either factory-installed default values or your choices. They allow the terminal to be configured according to your preference, and provide compatibility to the host and AC power source. Unlike some terminals, the VT100 family does not use switches or jumpers to individually turn the built-in features on or off. Instead, this family uses a nonvolatile memory (NVR) that always remembers what features have been selected, just as if a switch had been set.

Set-up features can be selected by the host or by you through your terminal’s keyboard. When Set-Up is entered, the status of the features stored in the nonvolatile memory are shown on the screen. These feature settings can either be stored permanently in the nonvolatile memory or stored temporarily until the terminal is turned off. Pressing SHIFT “S” during Set-up mode stores the current settings as permanent. The terminal operation reflects the current feature selections. If a recall operation is performed, the terminal is reset, or the terminal power is turned off, all temporary feature settings are replaced by the features that have been stored in NVR.

Set-Up

Set-Up mode provides two (or three for the VT131) brief descriptions of the current feature status. Set-Up A displays the location of the tab stops set in the terminal and a visual ruler that numbers each character position on the line. The status of other terminal features is summarized in Set-Up B.

Entering Set-Up A is achieved by pressing the SET-UP key. The bottom line of the display consists of a ruler, which numbers each character position available on a line. The location of each tab stop is shown by a “T” placed above the ruler. To change a tab, use the space bar to advance the cursor to any of the numbered character positions. Press the Set/Clear Tab keys (@/2 key) when you reach the position where you want to set or clear a tab. If there is a “T” present, the tab will be cleared. If no “T” is at that location, a tab will be inserted. Once you have finished, you may exit from Set-Up mode A by pressing the SET-UP key again.

Set-Up B mode only can be entered from Set-Up A mode. While in Set-Up A, press the 5 key on the main keyboard. This brings you into Set-Up B. See Figure 5-5.

To change any of the features shown in Figure 5-6, use your space bar to move the cursor to the feature you want to change. Once the cursor is positioned over the block to be changed, press the 6 key. This changes the bit to the opposite of what is displayed – either 1 or 0. After you have selected all the features you want, exit from Set-Up B mode by pressing the 5 key which returns you to Set-Up A mode, or press the SET-UP key again to exit Set-Up mode.

The next section describes the features you can change once you are in Set-Up B.

Receive Speed

When the terminal is in Set-Up B Mode, this key steps the terminal through the receive baud rate settings in ascending order.

Transmit Speed

When the terminal is in Set-Up B Mode, this key steps the terminal through the transmit baud rate settings in ascending order.

Scroll

Scrolling is the upward or downward movement of existing lines on the screen to make room for new lines at the bottom or top of the screen. When using jump scroll, new lines appear on the screen as fast as the host sends them to the terminal. Smooth scroll places a limit on the speed at which new lines of data can be sent to the terminal, but since the movement occurs at a smooth, steady pace, the data can be read as it appears on the screen.

Auto Repeat

Auto Repeat causes a key to be repeated automatically at the rate of approximately 30 characters per second when the key is held down for more than one half second. So if you need a certain character to be repeated, you don’t have to retype it.

Dark or Light Background

In the normal screen mode, the display contains light characters on a dark background. In the reverse screen mode, the display contains dark characters on a light background. You can select whatever screen mode is more comfortable for you.

Cursor

The cursor display is used to indicate the active position or where the next typed character will appear on the screen. You can select a block or underline cursor.

XON/XOFF

The VT100 family members are capable of automatically generating the synchronizing codes XON (DC1) and XOFF (DC3). The XOFF code tells the host to stop the transmitting of data. The XON code tells the host to resume transmitting data. This mode of operation is required when smooth scroll, set-up, or the printer port is to be used. It is also required for baud rates over 4,800 bits per second.

ANSI/VT52 Compatibility Mode

With ANSI mode, the VT100 family will respond to software based on ANSI standards – ANSI X3.4-1977, X3.41-1974, and X3.64-1979. VT52 compatibility mode lets the terminal respond to software written for use with Digital’s VT52 video terminal.

Keyclick

With this, you can choose to have a silent keyboard or hear an audible click each time a key is pressed.

Margin Bell

The margin bell functions just like the bell in a typewriter. When the margin bell is on, a tone will sound whenever the cursor is eight characters from the end of the current line.

Character Sets

Choose between US. and U.K. character sets. The VT100 family contains character sets for the United States and the United Kingdom. The only difference between these two character sets in one character, the # or the £ symbol. When the standard U.S. character set is selected, the uppercase 3 on the main keyboard displays the # character. The £ character is displayed when the U.K. character set is selected.

Automatic Wraparound

When this feature is selected, characters that would otherwise appear beyond the right margin are automatically placed in the first character position of the next line.

New Line

The new line feature enables the RETURN key on your terminal to function like the RETURN on an electric typewriter. When the new line feature is enabled, pressing the RETURN key generates the carriage return (CR) and the linefeed (LF) codes. When a linefeed code is received, the code is interpreted as a carriage return and a linefeed.

Interlace Mode

Interlacing allows you to display alternate rows of pixels in successive screen sweeps. Digital terminals are factory set with interlace mode disabled. Although Digital graphics applications do not require interlacing, this feature is user-selectable.

Power

During the initial installation, the terminal display must be set to either the 50 or 60 Hertz power line frequency. In the United States, it is set to 60 Hertz.

Bits Per Character

This feature allows the terminal to transmit and receive either 7- or 8-bit characters. When set for 8-bit operation, bit 8 is set to space or 0 for characters transmitted and is ignored for all characters received.

Parity

Parity, when enabled, checks for single-bit errors in data transmission. If a transmission error occurs, members of the VT100 family can often detect it and indicate its presence by placing a checkerboard character on the screen in place of the character with the error. When parity is disabled, no parity bit is transmitted or received.

Parity Sensing

This feature defines which method of parity checking – odd or even – is used. If the parity is turned off, the parity sense selection will be disregarded.

Baud Rates

Members of the VT100 family can transmit data at any one of the following speeds: 50, 75, 110, 134.5, 150, 200, 300, 600, 1200, 1800, 2000, 2400, 3600, 4800, 9600, or 19,200 bits per second.

These terminals are also capable of receiving data at any of the following defined speeds: 50, 75, 110, 134.5, 150, 200, 300, 600, 1200, 1800, 2000, 2400, 3600, 4800, 9600, or 19,200 bits per second. The receive speed is independent of the transmit speed. The terminal can receive data at one speed and transmit it at a different speed.

Answerback Message

Answerback is a feature that provides the terminal with the ability to identify itself by sending a message to the host. This message can be up to 20 characters in length, including control characters. The entire answerback message sequence can take place automatically without affecting the screen or requiring operator action if an ENQ is sent to the terminal. You can send the answerback message by pressing the CTRL and BREAK keys simultaneously.

To set the answerback message, use the following steps:

1. Place the terminal in Set-Up B mode.
2. Press the SHIFT and A keys simultaneously. The terminal will respond by placing A = on the screen.
3. Type the message delimiter character which may be any character not used in the actual answerback message. The message delimiter character is not part of the answerback message. If you make a mistake when typing the answerback message, type the message delimiter character again and go back to step 2. This is the only way to correct errors in the answerback message.
4. Type the answerback message. The message may be up to 20 characters, including space and control characters. Control characters will be displayed as a blackened diamond-shaped character to indicate their presence in the message.
5. Type the message delimiter character. Once the message delimiter character is typed, the answerback will disappear from the screen.

Once you have followed these steps, the answerback message will be temporarily stored in the terminal and can be saved with a Save operation.

Save Operation

You can change or store set-up features on either a temporary or fixed basis. To temporarily store a feature, just exit set-up mode after changing the feature – the terminal reacts according to the new setting. If a recall operation is performed, or the terminal is reset, or the terminal power is turned off, all temporary feature settings are replaced by the features that have been stored on a fixed basis.

If you want to store set-up feature settings on a permanent basis, follow the next two save operation steps. First, place the terminal in set-up mode. Second, press the SHIFT and S keys simultaneously. The screen will clear and the message “wait” will be displayed in the upper-left corner. After a few seconds, the terminal will automatically return to Set-Up A mode. You have now saved your set-up features in nonvolatile memory.

Recall Operation

It is possible for temporarily stored feature settings to differ from those stored on a fixed basis. If you want to return to the fixed settings, you can perform a recall operation. First, place the terminal in set-up mode. Next, press the SHIFT and R keys simultaneously. The screen will clear and the message “wait” will appear in the upper-left corner of the screen. After a few seconds, the terminal will return to Set-Up A mode. The VT102 and VT131 also have factory default settings that can be recalled with SHIFT “D”.

Printing

With the VT100’s optional printer port or the standard printer port found on the VT102, VT125, and VT131 terminals, you can attach your video terminal to a serial printer for hardcopy output.

Your video terminal determines if the serial printer is connected and ready to operate by the data terminal ready (DTR) interface signal of the printer. When the DTR signal of the printer is on, the printer is ready to print. If a printer is not connected, requests for printing are ignored.

If the printer is unable to print when a print operation is selected, print requests cause the video terminal to wait for the print operation to be completed or cancelled. During this time, the screen of the terminal will not display new characters. After the print operation is complete or cancelled, the screen displays new characters.

The printer may not be ready to print for one or more of the following reasons:

• AC power is turned off.
• The printer is off-line.
• The printer is out of paper.
• The printer is out of ribbon.
• The printer cover is open.
• The printhead is jammed.

Refer to the documentation provided with your printer to correct any of the above situations, or consult the appropriate chapter within this handbook.

Printing is performed using one of four print operations: auto print which prints one line at a time, print screen, printer controller, and print cursor line. All print operations can be selected by the host while the terminal is on-line. Only auto print and print screen operations can be selected from the video terminal’s keyboard. Keyboard-selected print operations are performed while the terminal is on-line or off-line. If the terminal is off-line, the KBD LOCKED indicator goes on until printing finishes. See your User Guide for more information.

Printing double-height and double-width characters results in printing the same line twice with single-height and single-width characters. Double-width characters are printed as single-width characters.

Auto Print

Auto print operation prints the current line before the cursor moves to the next line. The cursor moves to the next line when the terminal receives a linefeed, form feed, or vertical tab character. This character is also transmitted to the printer at the end of the printed line.

If the auto wrap feature is on, characters received when the cursor is at the right margin are automatically wrapped to the next line. Before the cursor moves to the next line, the current line is printed. The auto wrapped line ends with the carriage return and linefeed characters.

Select auto print using the following procedure. After verifying that the printer is ready to print, hold down the CTRL key and press the (PRINT)/ENTER key, and then release both keys. Although there is no visible indication on the screen, the current line is printed before the cursor moves to the next line. When selected, auto print operation continues until turned off.

If you want to stop printing, enter and exit set-up. The current line is not printed, but the auto print feature stays selected. To turn off auto print, hold down the CTRL key and press the (PRINT)/ENTER key, then release both keys.

Print Screen

The print screen command prints a copy of the screen. Depending on the print features chosen in set-up, the scrolling region or complete screen is printed. The scrolling region is the area of the screen between the top and bottom margins. The top and bottom margins are selected by the host.

Select the print screen feature with the following procedure:

• Verify that the printer is ready to print.
• Hold down the SHIFT key, and press the (PRINT)/ENTER key and release both keys. The characters displayed on the screen will be printed.
• To stop the print screen operation before printing is complete, enter and exit set-up.

In the case of both auto print and print screen operations, if printing has been stopped by entering and exiting set-up mode, move the printhead to the left margin. Refer to your printer’s documentation for information about local operating procedures used with the printer.

Printer Controller

Printer controller gives the host direct control of the printer. When printer controller is selected, characters received from the host are not displayed on the video screen. The characters are sent directly to the printer.

Print Cursor Line

This lets you print the current line without changing the cursor position.

Programming Information

Escape and control sequences provide functions not offered by control characters of the character set. These sequences are multiple character control functions that are not displayed but determine terminal operation. Escape and control sequences are defined by ANSI X3.41-1977 and X3.64-1979. Refer to Appendix B for more information about sequences and sequence formats or consult the User Guide for your terminal model.

Maintenance

The VT100 family of terminals is designed to be easy to maintain. No preventative maintenance is required. The terminals have built-in, self-test diagnostics that greatly reduce the time necessary to isolate and repair faults. They also feature automatic self-tests that are run every time the terminals are powered up. Refer to the User Guide for your terminal model for more information about self-tests, as well as descriptions of fatal and nonfatal errors. Should a repair become necessary, Digital Field Service is available worldwide.

The VT100 family has proven to be an exceptionally reliable series of terminals. There are just two mechanical switches – one for turning the terminal on, and one for selecting the power supply voltage. The use of pop fasteners instead of screw fasteners reduces the time and cost of repairs by providing easy access to all components. All other functions, such as baud rates, tabs, and parity, for example, are set via the keyboard and stored in the nonvolatile memory. The elimination of mechanical switches aids the use of diagnostics for testing the terminal functions and adapting to varying environments under host control.

Self-Test

A self-test mode is built into every VT100 family member. It automatically, or on command, tests the condition of the terminal should a fault be suspected. This self-test program checks the following items:

• Advanced video (if included)
• Nonvolatile memory
• Internal memory
• Keyboard

To invoke a self-test, you can:

• turn the terminal on, or
• hit the reset key while in set-up mode.

Operator Troubleshooting Checklist

If it appears that there is a problem in any member of the VT100 family of terminals, initiate the power-up self-test program. This test will help to determine if the problem lies in your terminal or in some other part of the computer system.

Terminal will not turn on when the power switch is set to ON.

• AC power cord is not plugged into the wall outlet. Plug in the cord.
• AC power cord is not plugged into the terminal. Plug in the cord.
• Power is not coming from the wall outlet. Check the outlet with a known working electrical device. If there is no power, contact an electrician.
• AC line fuse is blown. Turn off the terminal and have the fuse replaced.

No keyboard response.

• ON LINE or OFF LINE is not on and keyboard cable is not plugged into the monitor. Plug in the keyboard cable.
• KBD LOCKED indicator is on. Keyboard buffer is full and keyboard cannot accept any more characters since the computer sent the XOFF signal to the terminal. KBD LOCKED condition may be cleared be entering and exiting the set-up mode. Be careful that characters are not lost during this procedure. If this condition persists, check with host software documentation for a possible operating error.
• Perform the self-test.

ON LINE or OFF LINE indicator is on with no cursor on the screen.

• Screen brightness is too low. Enter set-up and increase screen brightness.

Garbled or error characters.

• Incorrect set-up feature. Possible set-up features that may be in error: ANSI/VT52 mode, auto XON/XOFF, bits per character, parity, parity sense, receiver speed, or transmit speed. Correct the set-up feature if it is in error and save them. Otherwise, the self-test may reset them to the saved NVR value.
• Perform the self-test operation.

Several successive long tones.

• The terminal has had difficulty in reading or writing the set-up features stored in nonvolatile memory. Check the feature settings and perform the save operation.
• Perform the self-test operation.

Terminal does not respond to typed characters.

• Screen cannot be updated by the computer, terminal transmitted XOFF. Press NO SCROLL button.

Additional Documentation

The following documents contain more detailed information about the VT100 family of terminals.

VT100 User Guide (EK-VT100-UG)

Describes the installation, operation, and programming of the VT100 terminal.

VT100 Mini Maintenance Manual (EK-VT100-J1)

Describes procedures to troubleshoot and repair the VT100 and VT125 terminals. Also identifies what various error codes mean.

VT100 Technical Manual (EK-VT100-TM)

Describes VT100 and VT125 terminals to detailed block level.

VT100 Illustrated Parts Breakdown (EK-VT100-IP)

Provides a detailed parts breakdown of the VT100 field replaceable units. Does not contain part numbers for components on the printed circuit boards.

VT100 Print Set (MP-00633)

Provides a complete set of electrical and mechanical schematic diagrams for the VT100 terminal.

Also of interest are:

PDP-11 and VAX Systems & Options Catalogs

Provide you with the most accurate and up-to-date information on currently available PDP-11 and VAX systems, options, and software products. These customer documents are designed to help you select the right Digital products for your needs. European versions are also available.

If you require information not contained in these documents, contact your local Digital representative, dealer, or distributor.

Specifications

Performance Characteristics

Display

Keyboard

Communications

Power Requirements

Operating Environment

Physical Characteristics

Monitor

Keyboard