This paper describes the design of the letter keyboard for the IBM SELECTRIC® Composer. The design requirements were to provide an information transfer mechanism not only for character selection using the SELECTRIC Typewriter printing system, but also for proportional escapement selection and print impact velocity control. The keyboard was required to be exceptionally reliable, to have the positive SELECTRIC Typewriter touch characteristics, and to be consistent with the keyboard layout standards that are familiar to the operator or typist.
The keyboard that has been developed has a completely serial operating sequence. Each event in a sequence is positively latched as it occurs, and remains latched until its function is completed. This insures reliable information transfer without compromising speed or input-signal storage capability.