The VT420 is an

ANSI standard The American National Standards Institute (ANSI ) is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organi ...

computer terminal A computer terminal is an electronic or electromechanical hardware device that can be used for entering data into, and transcribing data from, a computer or a computing system. The teletype was an example of an early-day hard-copy terminal and ...

introduced in 1990 by

Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president unt ...

(DEC). The 420 is the only model in the 400 series, replacing the

VT320 The VT320 is an ANSI standard computer terminal introduced by Digital Equipment Corporation (DEC) in 1987. The VT320 is the text-only version, while the VT330 adds monochrome ReGIS, Sixel and Tektronix 4010 graphics, and the VT340 adds color. ...

. There are no color or graphics-capable 400 series terminals; the VT340 remained in production for those requiring

ReGIS Regis or Régis may refer to: People * Regis (given name), a given name (including a list of people with the name) * Regis (surname), a surname (including a list of people with the name) * Regis (musician), full name Karl O'Connor, an English ...

and

Sixel Sixel, short for "six pixels", is a bitmap graphics format supported by terminals and printers from DEC. It consists of a pattern six pixels high and one wide, resulting in 64 possible patterns. Each possible pattern is assigned an ASCII chara ...

graphics and color support. The entire lineup of VT300s and VT420 was eventually replaced by the relatively unknown VT500 series starting in 1993.

Description

The VT420 is essentially an updated VT320, adding the multi-session capabilities originally introduced on the VT330 and VT340. Those two models include a system known as

TD/SMP TD/SMP, short for Terminal Device/Session Management Protocol, was a terminal multiplexer system introduced by DEC on their VT330/340 terminals in 1987. The terminal-side was referred to as SSU. TD/SMP allowed data from two separate host sessions ...

which allows two sessions to be multiplexed over a single serial connection to a compatible

terminal server A terminal server connects devices with a serial port to a local area network (LAN). Products marketed as terminal servers can be very simple devices that do not offer any security functionality, such as data encryption and user authentication. ...

. Alternately, the two sessions can be supported by separate serial connections on those models with multiple MMJ ports. Using either method, the VT330/340/420 can either show the two sessions behind each other, using a key sequence to flip back and forth, or split the screen horizontally to display the sessions one above the other, or vertically side-by-side. The VT420 also added a number of more minor features. One was to add a number of PC character sets, allowing the terminal to be used with a variety of PC programs. Another allows the terminal to generate the proper character sequences to produce rectangular-area commands. For instance, one can select a rectangular area and fill it with a particular character, or blank it out. This is in addition to the terminal-side editing system introduced on the VT300s. The VT420 has a total of 5 sets of 94 characters for normal VT operation, another 3 sets of 128 PC characters, and 1 set of 96 characters containing various graphics and math symbols. Like all models since the VT200 series, the user can also upload a custom character set of their own design using the

system. Likewise, it also supports the

National Replacement Character Set The National Replacement Character Set (NRCS) was a feature supported by later models of Digital's (DEC) computer terminal systems, starting with the VT200 series in 1983. NRCS allowed individual characters from one character set to be replaced b ...

system, which swaps out single characters in 7-bit modes to allow basic changes like swapping the for the for use on UK systems. All DEC terminals that came after the

VT100 The VT100 is a video terminal, introduced in August 1978 by Digital Equipment Corporation (DEC). It was one of the first terminals to support ANSI escape codes for cursor control and other tasks, and added a number of extended codes for special f ...

, including the VT420, are able to emulate their ancestors. The VT420 has

and

VT52 The VT50 was a CRT-based computer terminal introduced by Digital Equipment Corporation (DEC) in July 1974. It provided a display with 12 rows and 80 columns of upper-case text, and used an expanded set of control characters and forward-only scro ...

emulating modes. The screen itself is a 14" flat CRT with a resolution of 800 (horizontal) by 400 (vertical) pixels. A variety of glyphs are available that provide 80 or 132 characters across, and 24, 36 or 48 lines of text vertically. The screen has room for 25 lines at normal font sizes, but the last line was normally used for status indications, like . The MMJ ports can operate at speeds up to 38,400 bit/s, double that of the VT300s' maximum 19,200 bit/s.

Notes

References

Installing and Using the VT420 Video Terminal
DEC, 1990
VT420 Programmer Reference Manual
DEC, 1992

External links

*
vt100.net
{{Authority control DEC computer terminals Character-oriented terminal Computer-related introductions in 1990