Matrix keyboard polling control circuit - has cycled counter to address rows and columns using bistable control circuit for detecting multi-key actuation

摘要

The matrix keyboard polling circuit consists of a polling counter (3) driven by signals from an AND-gate (7) coupled to a clock generator (2) and keyboard control unit (5). The counter outputs are connected to two decoding stages. One decoding stage (Di) accesses NAND gates (6) coupled to the rows of the key matrix (1) and the other decoding stage (D2) accessing NAND gates connected to the columns of the matrix. Signals from the NAND gates provide a signal (5) and a complement (5') for two flip flops (FF1, FF2) in the control unit that ensures validity of the key actuation to generate a strobe output.