Ultra-low power, scan on demand keypad encoder

Details Ultra-low power, scan on demand keypad encoder Ultra-low power, scan on demand keypad encoder

1995-09-14

1996-07-23

Swarthout, Brent A.

Coded data generation or conversion

Bodily actuated code generator

Including keyboard or keypad

341 25, 341 26, 364707, H03M 122

Patent

active

055394000

ABSTRACT:
A keypad encoder is used with a keypad having an array of keys arranged in columns and rows. Depressing any key on the keypad closes a corresponding switch, coupling one of the columns to one of the rows. The keypad encoder includes a resettable logic circuit that generates a control signal having first and second states that control the mode of operation of the keypad encoder. A scanning circuit asserts a scanning signal on the columns of the keypad in a predefined sequence when the control signal is in the first state and asserts the scanning signal on all of the columns of the keypad simultaneously when the control signal is in the second state. An encoder circuit identifies which row, if any, has a closed switch in any of the keypad columns on which the scanning circuit has asserted the scanning signal. The encoder circuit also activates a keydown signal whenever any switch in any of the keypad columns on which the scanning circuit has asserted the scanning signal is closed and deactivates the keydown signal when none of the switches in any of the keypad columns on which the scanning circuit has asserted the scanning signal is closed. After a depressed key is sensed, its identity is stored in an output circuit, the control signal is put in the second state and the scanning circuit stops scanning the keypad. The scanning circuit resumes scanning the keypad only after another depressed key is detected by the encoder circuit.

REFERENCES:
patent: 4109315 (1978-08-01), Pan
patent: 4266278 (1981-05-01), Ebihara et al.
patent: 4305065 (1981-12-01), Mogi
patent: 4335374 (1982-01-01), Nyuji
patent: 4502038 (1985-02-01), Lowenthal et al.
patent: 5235331 (1993-08-01), Sato
patent: 5280283 (1994-01-01), Raasch et al.

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