Abstract: In a conventional 8×17 drive line/sense line keyboard switch matrix, a one-to-one correspondence between keyboard key switches and drive line/sense line pairs, together with a sequential driving of the drive lines, permits discrimination between 8×17=136 keyboard keys with 25 I/O pins. In contrast, the present invention utilizes drive line/sense line combinations to discriminate between keyboard keys with fewer total drive and sense lines, thereby reducing the number of required IC pin connections. In addition to achieving a reduction in the number of required pin connections, particular drive line/sense line contact patterns (e.g., a 2/2 pattern), and an associated subtraction algorithm, allow for efficient layouts of the drive lines and sense lines on respective membrane switch layers, a reduction of detection errors arising from inadvertent illegal simultaneous key presses, and discrimination of “special” simultaneous key press conditions.

Abstract: In a conventional 8×17 drive line/sense line keyboard switch matrix, a one-to-one correspondence between keyboard key switches and drive line/sense line pairs, together with a sequential driving of the drive lines, permits discrimination between 8×17=136 keyboard keys with 25 I/O pins. In contrast, the present invention utilizes drive line/sense line combinations to discriminate between keyboard keys with fewer total drive and sense lines, thereby reducing the number of required IC pin connections. In addition to achieving a reduction in the number of required pin connections, particular drive line/sense line contact patterns (e.g., a 2/2 pattern), and an associated subtraction algorithm, allow for efficient layouts of the drive lines and sense lines on respective membrane switch layers, a reduction of detection errors arising from inadvertent illegal simultaneous key presses, and discrimination of “special” simultaneous key press conditions.