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VT220

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VT220
DEC VT220 terminal withLK201keyboard
ManufacturerDEC
TypeComputer terminal
Release dateNovember 1983(November 1983)
Introductory priceUS$1,295(equivalent to $4,000 in 2023)
CPUIntel 8051@ 11.0592 MHz
Memory16 KB RAM
24 KB ROM
256 byteNVRAM
Display12 in (30 cm)CRT
80x24 characters
InputLK201keyboard
ConnectivityRS-232serial
20 mA current loop
DE-9serial printer port
PredecessorVT100
SuccessorVT320
DEC VT220 in use atThe National Museum of Computing
DEC VT240

TheVT200 seriesis a family ofcomputer terminalsintroduced byDigital Equipment Corporation(DEC) in November 1983.[1][2]TheVT220was the basic version, a text-only version with multi-lingual capabilities. TheVT240added monochromeReGISvector graphicssupport to the base model, while theVT241did the same in color. The 200 series replaced the successfulVT100series, providing more functionality in a much smaller unit with a much smaller and lighter keyboard. Like the VT100, the VT200 series implemented a large subset ofANSI X.364.Among its major upgrades was a number of international character sets, as well as the ability to define new character sets.

The VT200 series was extremely successful in the market. Released at $1,295,[3]but later priced at $795, the VT220 offered features, packaging and price that no other serial terminal could compete with at the time. In 1986, DEC shipped 165,000 units, giving them a 42% market share, double that of the closest competitor,Wyse.Competitors adapted by introducing similar models at lower prices, leading DEC to do the same by releasing the less-expensive $545VT300 seriesin 1987. By that time, DEC had shipped over one million VT220s.[4]

Hardware[edit]

The VT220 improved on the earlier VT100 series of terminals with a redesigned keyboard, much smaller physical packaging, and a faster microprocessor, theIntel 8051microcontroller.The VT220 was available withCRTsthat used white, green, or amberphosphors.

The VT100s, like theVT50sbefore them, had been packaged in relatively large cases that provided room for expansion systems. The VT200s abandoned this concept, and wrapped the much smaller 1980s-era electronics tightly around the CRT. The result was a truncated pyramidal case with the apex at the back, only slightly larger than the CRT. This made it much easier to fit the terminal on a desk.

Normally the monitor sat facing upward at about a 15 degree angle. Because it was lower than head height, the result was an especially ergonomic terminal. On the rear bottom of the case was a carrying handle that could also be used to angle the monitor more foward. An extendable post could do so to even greater angles, allowing the monitor to face directly forward.

TheLK201keyboard supplied with the VT220 was one of the first full-length, low-profile keyboards available; it was developed at DEC'sRoxbury,Massachusettsfacility. It was much smaller and lighter than the VT100s version, and connected to the terminal using a lighter and more flexible coiled cable and atelephone jackconnector.

The VT200s were the last DEC terminals to provide a20mA current loop serial interface(using a 8-pinMolex-style connector),, an older standard originally developed for thetelegraphsystem but became popular on computers due to the early use ofTeletype Model 33's asad hocterminals. A standard 25-pin D-connector was also provided for RS-232. Only one of the two ports could be in use at a given time. Later DEC terminals would replace both of these with their proprietaryModified Modular Jack(MMJ) connectors.

Another version of the terminal, the VT240, used DEC's ownDEC T-11,a single-chip microcontroller version of thePDP-11minicomputer.

DEC VT220 connected to theserial portof a modern computer.

Software[edit]

The VT220 was designed to be compatible with theVT100,but added features to make it more suitable for an international market. This was accomplished by including a number of differentcharacter setsthat could be selected among using a series of ANSI commands.

Glyphs were formed within a 10 by 10 grid. The terminal shipped with a total of 288 characters in its ROM, each one formed from an 8 by 10 pixel glyph. Using only 8 of the columns left space between the characters. The characters included the 96 printable ASCII characters, 67 Display Controls, 32 DEC Special Graphics, and a backward question mark used to represent undefined characters.

The VT200s included the ability to make minor changes to the character set using theNational Replacement Character Set(NRCS) concept. When operating on an8-bit cleanlink up to 256 character codes were available, which included a full set of European characters. But when operating on a typical 7-bit link, only 128 were available, and only 96 of these produced display output as the rest werecontrol characters.This was not enough characters to handle all European languages. Most terminals solved this by shipping multiple complete character sets inROM,but there was a cost in doing so.

DEC's solution to this problem, NRCS, allowed individual characters glyphs in the base set of 96 7-bit characters to be swapped out. For instance, the British set made a single substitution, replacing the US's hash character,#,with the pound sign,£.The terminal included 14 such replacement sets, most of which swapped out about a dozen characters.[5]This eliminated the need to ship 14 versions of the terminal, or to include 14 different 7-bit character sets in ROM.

Additionally, the VT200s allowed for another 96 characters in theDynamically Redefined Character Set(DRCS), which could be downloaded from the host computer. Data for the glyphs was sent by encoding a set of six vertical pixels into a single character code, and then sending many of theseSixelsto the terminal, which decoded them into the character set memory. In later models, the same sixel concept would be used to sendbitmapped graphicsas well. Character graphics were a common example of these downloaded sets.[6]

Escape Key controversy[edit]

Prior to the VT220, if anEscape keywas present, it was positioned in the upper left corner of the keyboard. The VT220 moved it to the typical location for the f11 key, in the middle of the top row of keys. For users of theTECOeditor, in which it is heavily used, this was inconvenient.[7][8]

Legacy[edit]

In 1983-1984, during the design phase of the IBMModel Mkeyboard, the VT220 was a new and very popular product. IBM's design team chose[9]to emulate its LK201 keyboard layout. Key innovations that IBM copied were the inverted-T shape of the arrow cluster, the navigation keys above it, and the numeric keypad off to its right. Eventually the popularity of the IBM PC would lead to the Model M layout becoming standardized by ANSI and ISO. Through those standards, minor variations of the VT220's keyboard layout have dominated keyboard design ever since.

See also[edit]

References[edit]

  1. ^Richard Shuford (1995–2005)."DEC Video Terminals".Archived fromthe originalon 2009-06-05.
  2. ^"VT220 Programmer Reference Manual".Digital Equipment Corporation.August 1984.
  3. ^Bartimo, Jim (21 November 1983)."DEC Unveils New Design In Successor To VT100".Computerworld.pp. 1, 6.Retrieved26 January2023.
  4. ^Bright, David (31 August 1987)."DEC VT320 late, but low price surprises".Computerworld.p. 16.Retrieved26 January2023.
  5. ^"National Replacement Character Set (NRCS)"[sic]
  6. ^VT320 Soft Character Sets
  7. ^Milton Campbell (April 1984). "The RT-11 Perspective: VT220".HARDCOPY.p. 170.
  8. ^"VT220 ESCAPE key".Computerworld.March 18, 1985. p. 68.you have to go hunt for the VT220 ESCAPE key
  9. ^"Why I Still Use a 34-Year-Old IBM Model M Keyboard".25 April 2020.Retrieved2021-04-19.

External links[edit]

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