Key input method and circuit

A key input circuit comprising:

• a plurality of switches provided between and matrix-connected to respective bits of an output port and respective bits of an input port;
• and
• control means for determining whether one or more of the plurality of switches has been manipulated, wherein the control means
• includes the output port and the input port,
• sets an initial state by rendering all of the bits of the output port in a first state and then determines whether one or more of the bits of the input port is in the first state,
• renders all of the bits of the output port in a second state when it is determined that one or more of the bits of the input port is in the first state;
• acquires first data indicating a manipulated one or ones of the plurality of switches by rendering, in order, the bits of the output port in the first state when it is determined that one or more of the bits of the input port is in the first state,
• acquires second data indicating a manipulated one or ones of the plurality of switches after a lapse of a predetermined amount of time, and
• makes the first and second acquired data effective if the first and second acquired data are identical.