JPS57125431A - Keyboard control circuit - Google Patents

Abstract

PURPOSE:To realize a keyboard strong against noise and reduce the cost of the device, by adopting the scanning system and by giving a simple constitution to the peripheral circuit of the keyboard. CONSTITUTION:A counter circuit 9 is counted up by a clock signal T1 given from a timing circuit 1, and the output signal of the counter circuit 9 is sent to a keyboard 2. When a key N in a key matrix 3 is depressed, key data is sent to a control circuit 11, and a output signal (d) is sent from the circuit 11 to a register 28. Meanwhile, the output signal corresponding to the key N from the counter circuit 9 is sent to a comparing circuit 29, and the circuit 29 gives a signal (b) of a wide pulse width to the circuit 11 if this output signal coincides with the signal stored in the register 28. Then, an interrupt signal RQE is outputted from the circuit 11 and is held in a register 31 of a keyboard data holding circuit 30. However, if another key is depressed before the key N is released, a signal ERROR is outputted from the circuit 11.