ADM-3A

ADM-3A

Developer	Lear Siegler

The ADM-3A was one of the first computer terminals manufactured by Lear Siegler. It had a 12 inch screen displaying 12 or 24 lines of 80 characters.

Lear Siegler, Inc. (LSI) manufactured its first video display (CRT for cathode ray tube) terminal in 1972 - the 7700A. In 1973 LSI hired a new head of engineering, Jim Placak. He and his team created the ADM-1 in late '73. ADM stood for American Machine. It set a new pricing low in the industry at $1,500. Its lower cost was primarily due to a unique single printed circuit board design. The ADM-1 was quickly followed by the ADM-2 in early '74. It had expanded functionality and a detached keyboard.

The famous clam shell ADM-3A quickly followed and the first manufactured units were shipped in mid 1974.

It set another new industry low single unit price of $1,195. Its innovative wave soldered single board design, which included the keyboard and all connectors, was packaged in an original clam shell enclosure.

In early 1973 the LSI division in Anaheim, CA that manufactured these products (and others) hired a dedicated management team for this product line - a VP, national sales manager, and one regional sales manager - for the western region. This regional manager was Dennis Cagan. He came from an LSI competitor. Within weeks of the launch of the ADM-3, Cagan started to book very large orders. It's 'Dumb Terminal' nickname came from some of the original trade publication ads, and quickly caught on industry wide. Due to two emerging trends the device immediately became the best selling in the industry. Computer communications speeds were rapidly increasing, and a wave of general purpose and dedicated single application minicomputer systems were hitting the market from dozens of manufacturers. These required inexpensive operator consoles that could match the speeds. With no fast low cost printers available, the ADM-3 (painted in a variety of custom colors for the OEMs) became the de facto standard.

Details

Originally priced at $1195, a DIY kit later sold for $995. The original model, the ADM-3, only displayed capital letters; this was supplanted by the ADM-3 version with both lower and upper case. The standard version of the terminal displayed only twelve (rather than twenty-four) rows of eighty characters. In those days RAM was expensive, and halving the display size halved the RAM requirement (and likewise all uppercase required only six bits per character to be stored rather than seven). Further optional add-ons included a graphics card enabling it to emulate a Tektronix 4014 and an extension port which would allow daisy chaining several ADM-3As on a single RS-232 line.

The ADM-3A's overall setup was controlled by 20 DIP switches under the nameplate at the front of the machine, beside the keyboard, including speed from 75 to 19,200 baud. The advanced configuration options allowed split speed connection, sending at one rate, and receiving at another.

Compared to the ADM-3, the ADM-3A was also much more controllable. It supported control codes to move the cursor around on the screen, and directly position the cursor at any point in the display. It did not, however, support “clear to end of line” or “clear to end of screen”, or other more advanced codes that appeared in later terminals, such as the VT52 and VT100.

Hardware

ADM-3A keyboard layout

The 5×7 dot matrix characters were displayed in amber, green, or white phosphor on black (the cursor was 7×9). The keyboard had 59 keys. The 12-inch monochrome CRT was mounted in the top half of the case, which was hinged in the back and opened like a clamshell. The CRT was typically made by Ball Brothers.

Unlike later terminals, such as the VT100, the ADM-3A did not use a microprocessor in its implementation, but instead used TTL. It did, however, use RAM chips, rather than the Circulating Memory used by earlier terminals, such as the Datapoint 3300.

Legacy

The use of the HJKL keys for moving the cursor in the vi editor and its descendants stems from the ADM-3A; it had the cursor-movement arrows printed on those four keys.

Both the arrows and the "home" correspond to the functions of the corresponding control characters Ctrl-H, Ctrl-J, Ctrl-K, Ctrl-L, and Ctrl-^ (identical to Ctrl-~) when sent to the terminal, moving the cursor left, down, up, right, and to the "home" position in the upper left-hand corner of the terminal, respectively. (The Ctrl-H and Ctrl-J functions were standard, but the interpretations of Ctrl-K, Ctrl-L, and Ctrl-^ were new to the ADM-3A.)

Finally, the control key was located above, not below, the shift key—in the same place where most modern PC keyboards put the Caps Lock key. Many standard Unix key combinations were designed with the QWERTY layout and the ADM-3A's original Ctrl key placement in mind. Many of those key combinations are still in use today, even on non-Unix operating systems. Seasoned computer users familiar with the original layout often claim that the different position of the Ctrl key on modern PC keyboard layouts makes the use of Ctrl key combinations more cumbersome. Solutions exist for many operating systems to switch around the Caps Lock and Ctrl keys in software, thus making the PC keyboard layout more closely resemble the ADM-3A's keyboard layout.

External links

• Lear Siegler ADM-3A on the terminals wiki
• Lear Siegler ADM 3A
• Lear Siegler, Inc. (LSI) Terminal ADM3A
• Digital Engineering, Inc. Retrographics RG-512