ASCII keyboard

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An ASCII keyboard is a keyboard that outputs codes in the ASCII standard character set. (American Standard Code for Information Interchange) ASCII keyboards were often off-the-shelf parts for embedding into computer systems, often producing signals at chip-compatible levels over seven parallel signal lines.

The layout of the ASCII character set was matched to a standard keyboard layout (based on American typewriters of the time) so that holding the Shift key could only flip a bit in the code to change between normal and shifted symbols. A different bit is flipped for alphabetic keys and keys on the numeric row.

Likewise, the Control key also flipped a bit in the ASCII code, producing an ASCII control code when used together with an alphabetic key. ASCII abbreviations for control codes ("FF", "BEL" etc) were sometimes printed on the corresponding alphabetic keys.

The ASCII character set had also inherited separate Carriage Return and Linefeed symbols from previous TeleType code sets, with both being used in sequence to encode a new line. ASCII keyboards therefore often had separate Return and Linefeed keys.

The ASCII character set is still in wide use, being the basis for practically all new character sets from the 1970's onwards, including the first 128 code points of Unicode. The American typewriter convention later changed somewhat and became the basis for the US-ANSI keyboard layout with a somewhat different order of the shifted symbols on the numeric row than of that in ASCII.