Saturday, November 22, 2008

Lear Siegler ADM-3A

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. Originally priced at $1195, a DIY kit later sold for $995. At first only allowing capital letters as ADM-3; the model was quickly supplanted by the more advanced version with both lower case, and uppercase. 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 setup was controlled by 32 DIP switches under the nameplate at the front of the machine, beside the keyboard, including speed from 75 to 19200 bit/s (although all speeds above 9600 were purely theoretical, as it could accommodate such speeds only if the actual incoming characters were coming at a much slower rate to accommodate its buffer, otherwise data would be lost). The advanced configuration options allowed split speed connection, sending at one rate, and receiving at another.

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