Chapter 7
The VT125 Graphics Terminal combines a bit map graphics architecture and the versatile alphanumeric features of the VT100 Video Terminal. It is designed for use in business graphics, and laboratory and scientific applications. As a financial analysis or business data tool, the VT125 is capable of plotting trend lines, bar charts and pie charts. In engineering laboratory applications, it can be used for point plot graphs, and strip charts. To support programs written for the VT105, the VT125 includes a VT105 emulator.
The VT125 is a microprocessor-based terminal that directly executes Digital’s general-purpose graphics descriptor, ReGIS (Remote Graphics Instruction Set). ReGIS allows the creation and storage of pictorial data as simple ASCII text. ReGIS is designed for efficient communication of graphics data to remote displays.
As a companion product to the VT125 terminal, Digital offers the Letterprinter 100 (Chapter 10), the LA50 Personal Printer (Chapter 12), or the DECwriter Correspondent (Chapter 13). Together, the terminal and printer provide you with a complete graphics package that is both powerful and easy to use.
Currently available models of the VT125 include:
The following features are unique to the VT125 Graphics Terminal:
Graphics capabilities in the ReGIS firmware include:
ReGIS, a graphic descriptor, is a symbol system that describes the parts of a picture. A picture (graphic) is the best way to communicate some types of information. A requirement for a graphic descriptor is to describe the picture with as few symbols as possible to save storage space and communication line time. ReGIS works by considering a picture to be a group of graphic objects. Each graphic object is a standard geometric shape that can be described with a few characters of information. For example, ReGIS understands that the shape of a circle applies to any circle that can be drawn. A circle can be described on the screen by the location of its center and a point on its circumference. The same type of understanding for other graphic objects allows ReGIS to be a compact descriptor of graphic images.
The VT125 Graphics Option can display 184,320 pixels in a 768-by-240-by-2 array and is considered a medium resolution device. The Graphic Option memory can store 196,608 pixels in a 768-by-256-by-2 array. The display of the VT125 is a window that looks into this memory. The window can move in any direction with a screen command to display all parts of the pixel memory, or move an object in the image to the center of the display.
The VT125 Graphics Terminal is a VT100 text terminal with a factory installed Graphics Option. Other options are listed below.
| Part Number | Description |
|---|---|
| VT1XX-AB | Advanced video option for VT100 or VT125. Adds the following features to the text terminal capabilities of the VT125: four alternate character attributes – bold, underline, reverse video, and blink – which can be selected in any combination on a character-by-character basis; extra memory to display a total of 24 lines in either 80 or 132 column format; provision for alternate character sets, which may also be selected on a character-by-character basis. |
| VT1XX-CA | VT101/VT102/VT131/VT125 20 mA current loop option with cable |
| VT1XX-CE | Upgrade kit to convert your VT100 or VT125 to word processing keyboard. |
NOTE
The printer port VT1XX-AC cannot be used on the
VT125 and is not required since a printer port is included with the VT125.
The following VT125 accessories and supplies are available. Check with your sales representative of Digital’s Installed Base Group for the latest information.
| Part Number | Description |
|---|---|
| 4A-VT125-00 | VT125 spares kit |
The VT125 has the same monitor, keyboard, and audible and visual controls and indicators as other members of the VT100 family. See Chapter 5 or VT125 User Guide.
All VT100 family members incorporate features that can be selected in set-up. Set-up features determine how the terminal operates. 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 on or off the built-in features. Instead, these terminals use a nonvolatile memory (NVR) that always remembers what features have been selected, just as if a switch had been set.
Set-Up mode provides two 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.
See Chapter 5 for details on entering Set-Up A.
As described in Chapter 5, Set-Up B mode only can be entered from Set-Up A Mode. Because the VT125 Graphics Terminal has features not included with a regular VT100 terminal, Set-Up B has additional features for you to select.
In addition to all the set-up features described in Chapter 4 for the VT100 family, the VT125 has two additional set-up features.
This switch sets the auxiliary port to match the character length of your printer or other serial device. When set to eight bits, the eighth bit is a space. (This is the same as 7S or 8N on other vendors’ terminals.) Note: Only on VT125.
This sets the auxiliary port to one of four baud rates: 300, 1200, 2400, and 9600. Set the speed to match the speed of your auxiliary device. Note: Only on VT125.
The VT125 is a serial line interface video terminal. It communicates asynchronously over full-duplex lines. All communications features are keyboard-selectable. Transmit and receive speeds can be set independently at 16 different rates from 50 to 19,200 baud. An EIA RS232-C compatible interface is standard. A 20 mA current loop interface is optional.
The VT125 Graphics Terminal can be connected to a computer directly or through a common carrier facility (telephone line). In both applications, either the Electronic Industry Association (EIA) interface provided with the terminal or the 20 mA current loop interface option are used.
When connecting the terminal to the computer through a telephone line, a modem or acoustic coupler is needed. The modem or acoustic coupler changes the serial characters transmitted between terminal and computer into signals that can be transmitted over the telephone line. Several types of modems can be used with the VT125 terminal. However, the modem used by the terminal must be compatible with the modem used by the computer.
The VT125 Terminal responds to three different programming standards:
Consult Appendix D or your VT125 User Manual for detailed information on escape sequences and sequence formats.
The VT125 has an automatic internal self-test that checks the terminal for correct operation every time the power is turned on. The VT125 is easy to maintain. No preventative maintenance is necessary. If a repair should be required, Field Service is available worldwide. The terminal is designed to make machine access and the replacement of parts fast and easy.
The VT125 terminal has several self-tests available for checking the operation of the terminal.
To prepare for all the tests except the power-up test, prepare the terminal by first pressing the power switch to the OFF position. Then disconnect the communications cables from the computer and auxiliary data ports. Third, if a cable was connected to the EIA computer port connector, install an EIA loopback connector on the EIA connector. If the cable was connected to the 20 mA connector, then install the loopback connector that was included with that option. Do not use the EIA loopback connector at the same time as the current loopback connector. Finally, turn the power switch ON. Note: To perform auxiliary port tests, consult your VT125 User Guide for details.
If it appears that there is a problem in the terminal, 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 does not respond to typed characters. Keyclicks are generated and keyboard indicators function.
The following documents contain more detailed information about the VT125 family of terminals.
Also of interest are:
If you require information not contained in these documents, contact your local Digital representative, dealer, or distributor.
For specifications on characteristics common to all VT100 family members, see Chapter 5.
| VT125 Graphics format | 768 horizontal × 240 vertical addressable points, two planes 768 × 480 logical address range for 2:1 picture aspect ratio |
| Composite video output
Composite video output provides RS170 output with the following nominal characteristics: |
|
| Output impedance | Equals 75 ohms. DC coupled sync level = 0 V |
| Black level | Equals approximately 0.3 V when loaded with 75 ohms |
| White level | Equals approximately 1.0 V with a 75 ohm load |
| Composite sync waveform | Meets EIA RS170 standards |
| Vertical interval | composed of six equalizing pulses, six vertical sync pulses, and six more equalizing pulses |
| Vertical interval timing | Equalizing pulse width = 2.33µs ± 50ns Vertical pulse width = 27.28µs ± 200ns Horizontal pulse width = 4.71µs ± 50ns Horizontal blank width = 11.84µs ± 50ns/80 column mode 12.34µs ± 50ns/132 column mode Front porch = 1.54µs ± 50ns |
An analog signal applied to the video input will be “ORed” with the internal video signal so the beam intensity at any point on the screen will correspond to the intensity of that signal. This would tend to make the beam brighter at that point. A video signal on this input affects only the internal screen and does not appear on the composite video output. This input has the following nominal characteristics:
| Input impedance | 75 ohms, DC coupled |
| Black level | 0 V |
| White level | 1.0 V |
| Maximum continuous input | ± 2.0 V |
The external video source must be synchronized to the VT125. It may do this by referencing the composite sync on the composite video output. This means that the video input will not synchronize with any composite video source.
| RGB | DC coupled analog signal |
| Output impedance | 75 ohms |
| Level ranging | 0-1 volt |
| Synchronization | None embedded |