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The VT50 is a
CRT CRT or Crt most commonly refers to: * Cathode-ray tube, a display * Critical race theory, an academic framework of analysis CRT may also refer to: Law * Charitable remainder trust, United States * Civil Resolution Tribunal, Canada * Columbia ...
-based
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 ...
that was introduced 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) in July 1974. It provided a display with 12 rows and 80 columns of upper-case text, and used an expanded set of
control character In computing and telecommunications, a control character or non-printing character (NPC) is a code point in a character encoding, character set that does not represent a written Character (computing), character or symbol. They are used as in-ba ...
s and forward-only scrolling based on the earlier VT05. DEC documentation of the era refers to the terminals as the DECscope, a name that was otherwise almost never seen. The VT50 was sold only for a short period before it was replaced by the VT52 in September 1975. The VT52 provided a screen of 24 rows and 80 columns of text and supported all 95
ASCII ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...
characters as well as 32 graphics characters, bi-directional scrolling, and an expanded control character system. DEC produced a series of upgraded VT52s with additional hardware for various uses. The VT52 family was followed by the much more sophisticated
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 ...
in 1978.


Description

These terminals supported
asynchronous communication In telecommunications, asynchronous communication is transmission of data, generally without the use of an external clock signal, where data can be transmitted intermittently rather than in a steady stream. Any timing required to recover data fro ...
at
baud In telecommunications and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulat ...
rates up to 9600
bits per second In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction ...
and did not require any fill characters. Like other early DEC terminals they were equipped with both an
RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such as a compu ...
port as well as a 20mA current loop, an older serial standard used with
teletype A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point-to-point and point-to-multipoint configurations. Init ...
machines that was more suitable for transmission over long runs of
twisted-pair Twisted pair cabling is a type of communications cable in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted balanced ...
wiring. Data was read into a small buffer, which the display hardware periodically read to produce the display. Characters typed on the keyboard were likewise stored in a buffer and sent over the serial line as quickly as possible. To interpret the commands being sent in the serial data, it used a primitive
central processing unit A central processing unit (CPU), also called a central processor, main processor, or just processor, is the primary Processor (computing), processor in a given computer. Its electronic circuitry executes Instruction (computing), instructions ...
(CPU) built from small-scale-integration
integrated circuits An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...
. It examined the data while the display hardware was inactive between
raster scan A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image s ...
lines, and then triggered the display hardware to take over at the appropriate time. The display system returned control to the CPU when it completed drawing the line. The CPU was so basic that addition and subtraction could only be done by repeatedly incrementing or decrementing two registers. Moreover, the time taken by such a loop had to be nearly constant, or text lower on the screen would be displayed in the wrong place during that refresh. Typing a character produced a noise by activating a relay. The relay was also used as a buzzer to sound the
bell character A bell character (sometimes bell code) is a device control code originally sent to ring a small electromechanical bell on tickers and other teleprinters and teletypewriters to alert operators at the other end of the line, often of an incoming ...
, producing a sound that "has been compared to the sound of a '52 Chevy stripping its gears." DEC also offered an optional hard-copy device called an
electrolytic An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble salts, acids, and bases, dissolved in a polar solvent like water. Upon dissolving, the ...
copier, which fit into the blank panel on the right side of the display. This device was able to print, scan-line by scan-line, an exact replica of the screen onto a damp roll of special paper. It did this by electroplating metal from an electrode into the paper. The paper ran between two electrodes. The electrode on one side was a thin straight bar oriented across the paper width. The electrode on the other side was a thin helical bar wrapped around a rotating drum. One rotation of the drum scanned an intersecting area of the electrodes across the width of the paper. While the copier did an admirable job of capturing the contents of the screen, the output of the copier had an unfortunate resemblance to wet toilet tissue. Digital patented the innovation of having a single
character generator A character generator, often abbreviated as CG, is a device or software that produces static or animated text (such as news crawls and credits rolls) for keying into a video stream. Modern character generators are computer-based, and they can ...
provide the text
font In metal typesetting, a font is a particular size, weight and style of a ''typeface'', defined as the set of fonts that share an overall design. For instance, the typeface Bauer Bodoni (shown in the figure) includes fonts " Roman" (or "regul ...
for both screen and copier. The basic layout of the terminal, with the screen and main keyboard on the left and the blank area on the right, was intended to allow the system to be upgraded. The printer was one such upgrade, but over time DEC offered a number of other options. The large size of the cabinet was deliberate, to avoid a cooling fan. The two circuit boards with processor and memory at the base of the terminal, and a single board with power-supply and monitor electronics at the rear, were cooled by
convection Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoy ...
. The large, flat top of the terminal frequently accommodated large volumes of DEC documentation, which could block the vents and cause overheating.


Versions


VT50

The VT50 was the first terminal Digital produced in this cabinet. It provided only 12 lines of text with blank lines between them to use the entire vertical area of the display. Like its predecessor, the VT05, the VT50 did not support lowercase letters. Computer users of that era seldom needed lowercase text.


VT50H

The VT50H added a separate "auxilary keyboard" on the right side of the original keyboard. This was arranged in the fashion of a
numeric keypad A numeric keypad, number pad, numpad, or ten key, is the calculator-style group of ten numeric keys accompanied by other keys, usually on the far right side of computer keyboard. This grouping allows quick number entry with right hand, ...
with additional
control key In computing, a Control key is a modifier key which, when pressed in conjunction with another key, performs a special operation (for example, ). Similarly to the Shift key, the Control key rarely performs any function when pressed by itself. ...
s above the numbers. Four of these were
cursor key Arrow keys or cursor movement keys are keys on a computer keyboard that are either programmed or designated to move the cursor in a specified direction. The term "cursor movement key" is distinct from "arrow key" in that the former term may r ...
s which sent through for up, down, left and right, respectively. Another three of the keys were unlabeled and could be programmed to return any two-character code, and would default to through .


VT52

The VT50 was soon replaced by the greatly upgraded VT52. The VT52 had considerably larger buffers, giving it the capacity to store not only a full 24 lines of text that better utilized the screen space, but also the text off the top and bottom of the screen. This allowed the terminal to scroll backwards a limited amount without having to ask the host to re-send data. Another significant upgrade was that the VT52 included lowercase text support. Many new commands and features were added: * Support for the , and characters, when the shift key was used with , or , respectively. * Typing on the numeric keypad could now be distinguished from the main keyboard by turning on Alternate-Keypad Mode. This returned multi-character codes, through . * New cursor control codes to support host-directed full-screen editing and a
WYSIWYG In computing, WYSIWYG ( ), an acronym for what you see is what you get, refers to software that allows content to be edited in a form that resembles its appearance when printed or displayed as a finished product, such as a printed document, web ...
display. * A "graphics character set" which included several less-common characters as well as the ability to print some fractions in-line, like . One notable feature was the introduction of a separate function keypad with the " Gold Key", which was used for editing programs like
WPS-8 WPS-8 is a Word Processing System sold by Digital Equipment Corporation for use with their PDP-8 processors (including the VT78, VT278 DECmate, and PC238 DECmate II and PC24P DECmate III microcomputer systems). WPS-8 supports a variety of 24 ro ...
, KED, and EDT. Pressing the Gold Key and then typing one of the keys on the keyboard sent a command sequence back to the host computer.


VT55

The VT55 incorporated an add-on graphics system that was capable of displaying two mathematical functions or
histogram A histogram is a visual representation of the frequency distribution, distribution of quantitative data. To construct a histogram, the first step is to Data binning, "bin" (or "bucket") the range of values— divide the entire range of values in ...
s. This was invoked by sending a command string that sent the terminal into ''graphics mode'', with further data being sent to a separate buffer and CPU. Both systems mixed their data during the display, allowing the user to mix graphics and text on a single screen, as opposed to systems like the Tektronix 4010 or
plotter A plotter is a machine that produces vector graphics drawings. Plotters draw lines on paper using a pen, or in some applications, use a knife to cut a material like Polyvinyl chloride, vinyl or leather. In the latter case, they are sometimes k ...
s that had to slowly draw text using graphics commands. This system became known as waveform graphics, and would re-appear on the later VT105.


Block mode versions

The VT61 and VT62 were block-mode terminals. The VT62 was to be used in conjunction with TRAX, a transaction processing operating system on high-end
PDP-11 The PDP–11 is a series of 16-bit minicomputers originally sold by Digital Equipment Corporation (DEC) from 1970 into the late 1990s, one of a set of products in the Programmed Data Processor (PDP) series. In total, around 600,000 PDP-11s of a ...
s. They used the same cabinet but had a more complete custom processor. Application-specific behavior was coded in separate
PROM A promenade dance or prom is a formal dance party for graduating high school students at the end of the school year. Students participating in the prom will typically vote for a ''prom king'' and ''prom queen''. Other students may be honored ...
memory, using a separate instruction code that the processor interpreted. This unpublished language was to be used to easily develop additional models specific to single Digital marketing organizations. These terminals synthesized a "tock" sound on a speaker for feedback when a key was pressed instead of the relay. Though the keyboards were identical, VT6x users admired the superior "feel".


VT78

The relatively large expansion area of the VT50 case, combined with rapidly shrinking electronics in the late 1970s, allowed DEC to produce single-box, stand-alone
minicomputer A minicomputer, or colloquially mini, is a type of general-purpose computer mostly developed from the mid-1960s, built significantly smaller and sold at a much lower price than mainframe computers . By 21st century-standards however, a mini is ...
/terminals similar to a contemporary
microcomputer A microcomputer is a small, relatively inexpensive computer having a central processing unit (CPU) made out of a microprocessor. The computer also includes memory and input/output (I/O) circuitry together mounted on a printed circuit board (P ...
. The VT78 added a single-chip
PDP-8 The PDP-8 is a family of 12-bit minicomputers that was produced by Digital Equipment Corporation (DEC). It was the first commercially successful minicomputer, with over 50,000 units sold during the model's lifetime. Its basic design follows the pi ...
processor to the VT52, ran a variant of Digital's
OS/8 OS/8 is the primary operating system used on the Digital Equipment Corporation's PDP-8 minicomputer. PDP-8 operating systems which precede OS/8 include: * R-L Monitor, also referred to as MS/8. * P?S/8, requiring only 4K of memory. * PDP-8 4K ...
operating system, and usually
WPS-8 WPS-8 is a Word Processing System sold by Digital Equipment Corporation for use with their PDP-8 processors (including the VT78, VT278 DECmate, and PC238 DECmate II and PC24P DECmate III microcomputer systems). WPS-8 supports a variety of 24 ro ...
, Digital's
word processing A word processor (WP) is a device or computer program that provides for input, editing, formatting, and output of text, often with some additional features. Word processor (electronic device), Early word processors were stand-alone devices dedicate ...
system.


Escape sequences

VT52 codes remained proprietary to DEC, although a number of other companies provided emulations in their terminals. Later VT series terminals supported a subset of these commands. One interesting case is the
GEMDOS GEM (for Graphics Environment Manager) is a discontinued operating environment released by Digital Research in 1985. GEM is known primarily as the native graphical user interface of the Atari ST series of computers, providing a WIMP desktop. I ...
system and its offshoot, the TOS operating system of the
Atari ST Atari ST is a line of personal computers from Atari Corporation and the successor to the company's Atari 8-bit computers, 8-bit computers. The initial model, the Atari 520ST, had limited release in April–June 1985, and was widely available i ...
. These systems used a VT52-based screen driver in an era when
ANSI escape code ANSI escape sequences are a standard for in-band signaling to control cursor location, color, font styling, and other options on video text terminals and terminal emulators. Certain sequences of bytes, most starting with an Escape character#ASC ...
s had already become almost universal. This version added several new commands including the ability to select colors.


Standard commands

VT52 commands normally consisted of the escape character and a single character following it. The exception to this rule was the Y command, which also required two numbers to be sent.


Cursor positioning

The code was used to position the cursor anywhere on the screen, using two parameters representing the X and Y coordinates of the cursor position, with the upper left corner of the screen being position 1,1. These numbers were sent as ASCII characters of that value, adding 31. For instance, to position the cursor at column 30 and line 20, you would add 31 to each value to get 61 and 51, then look up those ASCII characters, and . The complete command would then be (note the row, column ordering, not X, Y). Adding 31 ensures that the characters are shifted out of the control range into the printable character range, so they will transmit properly.


Terminal identifier codes

The command allowed the host computer to identify the capabilities of the terminal. There were eight possible responses.


Copier codes

Several additional codes were used with the optional copier:


Graphics mode

The VT52 and VT55 included two characters sets, ASCII and "graphics mode" which switched out the lower case characters and some punctuation with new characters useful for the display of math. Unusual were glyphs for ¹⁄, ³⁄, ⁵⁄, ⁷⁄, which could be combined with subscript numbers to produce things like ⅗, and scan lines allowing a function to be plotted with 8 times higher vertical resolution than text.


VT52 compatibility mode

Later VT terminals supported VT52 commands, as well as adding a single new command to return to full ANSI mode. Compatibility mode changed the response to the command; all models responded with the code .


GEMDOS/TOS extensions

The GEMDOS version of the VT52 command set adds a number of new commands. These mostly concerned color support, with the color selection being sent as a single character using the same number-to-character encoding as the command. Only the last four bits of the number were used, providing support for 16 colors. The Atari ST only supported 4 of those in 80 column mode and all 16 in 40 column mode. A few new cursor commands were added as well, essentially filling out the set of the original VT52 by including commands that cleared toward the top of the screen instead of the bottom."The VT-52 Emulator"
/ref> The system did not support a number of VT52 commands, including F, G and Z.


Notes


References


Citations


Bibliography

* *


External links


VT100 net

DEC VT52
Terminals Wiki
DEC VT55
Terminals Wiki
DEC VT62
Terminals Wiki
DEC corporate chronological product and financial summary, brief description and cropped image of VT52 on page 51, brief descriptions of VT55 and image with electrolytic copier visible on pages 51 and 59
* {{Digital Equipment Corporation DEC computer terminals VT052 Computer-related introductions in 1975