The VT420 is an
ANSI standard 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. Most early computers only had a front panel to input or display ...
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 until ...
(DEC). The 420 is the only model in the 400 series, replacing the
VT320. There are no color or graphics-capable 400 series terminals; the VT340 remained in production for those requiring
ReGIS and
Sixel 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 which allows two sessions to be multiplexed over a single serial connection to a compatible
terminal server. 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
Sixel system. Likewise, it also supports the
National Replacement Character Set 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, including the VT420, are able to emulate their ancestors. The VT420 has
VT100 and
VT52
The VT50 is a CRT-based computer terminal that was 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 forwar ...
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