Editing VT52 (section)

== Description ==
These terminals supported [[asynchronous communication]] at [[baud]] rates up to 9600 [[bits per second]] and did not require any [[fill character]]s. Like other early DEC terminals they were equipped with both an [[RS-232]] port as well as a [[Digital current loop interface|20mA current loop]], an older serial standard used with [[teletype]] machines that was more suitable for transmission over long runs of [[twisted-pair]] 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]] (CPU) built from small-scale-integration [[integrated circuits]]. It examined the data while the display hardware was inactive between [[raster scan]] 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]], producing a sound that "has been compared to the sound of a [[Chevrolet|'52 Chevy]] stripping its gears."<ref name="TNHD">{{cite book | title = The new hacker's dictionary | page=186 | editor1-last = Raymond | editor1-first = Eric S. | editor1-link = Eric S. Raymond | publisher = [[MIT Press]] | year = 1996 | isbn = 978-0-262-68092-9 | url = https://books.google.com/books?id=g80P_4v4QbIC&pg=PA186 }}</ref>

DEC also offered an optional hard-copy device called an [[electrolytic]] 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.<ref>[http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/terminal/vt52/EK-VT52-MM-002_maint_Jul78.pdf VT52 DECscope Maintenance Manual]</ref><ref>{{Cite web|url=https://patents.google.com/patent/US4080609/en?oq=digital+equipment+corporation+electrolytic|title=Electrolytic recorder with additional helical cleaning stylus}}</ref> 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]].<ref>{{cite web |url=http://alt.nntp2http.com/sys/pdp11/2007/06/7fe45444f712cbc6e132f37362dc99cc.html |url-status=dead |archive-url=https://web.archive.org/web/20110714190507/http://alt.nntp2http.com/sys/pdp11/2007/06/7fe45444f712cbc6e132f37362dc99cc.html |archive-date=2011-07-14 |title=Re: Strange VT50 Decscope}}</ref><ref>{{Cite web|url=https://www.mail-archive.com/linux-advocacy@senator-bedfellow.mit.edu/msg02082.html|title=Linux-Advocacy Digest #457|website=www.mail-archive.com}}</ref>  Digital patented the innovation of having a single [[character generator]] provide the text [[font]] 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]]. The large, flat top of the terminal frequently accommodated large volumes of DEC documentation, which could block the vents and cause overheating.