INPUT CONTROL CIRCUIT

PURPOSE:To properly perform a signal processing corresponding to the kind of an input signal by outputting the input signal after confirming that the input signal has the same logical value continuously for the shift period of a specified number of digits of a shift registers. CONSTITUTION:The input signal X is read in the shift register 2 and shifted sequentially. Outputs D1-D4 of EXOR circuits 3a-3d to which couples of output signals B0-B4 are inputted are 1 when their inputs coincide with each other or 0 when not. Then when outputs C1 and C2 of the register 4 are set to 1 and C3 and C4 are set to 0 with a signal DATA, AND circuits 5c and 5d output 0 at all times and outputs E1 and E2 of circuits 5a and 5b are 0 when inputs D1 and D2 are 0. Namely, when logical values of the signals B0-B2 are all 0, the output F of an OR circuit 6 is 0 and an AND circuit 7 outputs a signal G of 1 when a signal F and a clock signal are both 0. An FF8, therefore, reads the signal B0 is when the signal G is 1 and holds it as a signal Y. A tri-state buffer 9 outputs the signal Y as the signal Y1 according to a specification output RD.