![]() 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 plotters that had to slowly draw text using graphics commands. 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. The VT55 incorporated an add-on graphics system that was capable of displaying two mathematical functions or histograms. It was the first DEC terminal that allowed WYSIWYG ("What you see is what you get") text editing. The VT52 also included lowercase text support and a host of other new features. This allowed the terminal to scroll backwards a limited amount without having to ask the host to re-send data. ![]() 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. The VT50 was soon replaced by the greatly upgraded VT52. Computer users of that era seldom needed lowercase text. Like its predecessor, the VT05, the VT50 did not support lowercase letters. It provided only 12 lines of text with blank lines between them to use the entire vertical area of the display. The VT50 was the first terminal Digital produced in this cabinet. The large, flat top of the terminal frequently accommodated large volumes of DEC documentation, which could block the vents and cause overheating. 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 size of the cabinet was deliberate, to avoid a cooling fan. The printer was one such upgrade, but over time DEC offered a number of other options. 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. Digital patented the innovation of having a single character generator provide the text font for both screen and copier. 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. One rotation of the drum scanned an intersecting area of the electrodes across the width of the paper. The electrode on the other side was a thin helical bar wrapped around a rotating drum. The electrode on one side was a thin straight bar oriented across the paper width. It did this by electroplating metal from an electrode into the paper. This device was able to print, scan-line by scan-line, an exact replica of the screen onto a damp roll of special paper. Pressing the Gold Key and then typing one of the keys on the keyboard sent a command sequence back to the host computer.ĭEC also offered an optional hard-copy device called an electrolytic copier, which fit into the blank panel on the right side of the display. One notable feature of the VT50 was the introduction of a separate function keypad with the " Gold Key", which was used for editing programs like WPS-8, KED, and EDT. 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. The CPU was so basic that addition and subtraction could only be done by repeatedly incrementing or decrementing two registers. The display system returned control to the CPU when it completed drawing the line. 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. 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. ![]() Characters typed on the keyboard were likewise stored in a buffer and sent over the serial line as quickly as possible. Data was read into a small buffer, which the display hardware periodically read to produce the display. Like other early DEC terminals, the VT50 series were equipped with both an RS-232 port as well as a 20mA current loop, an older serial standard used with teletype machines that was more suitable for transmission over long runs of twisted-pair wiring. The VT50 supported asynchronous communication at baud rates up to 9600 bits per second and did not require any fill characters.
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