| 摘要 |
PURPOSE:To select only an effective signal, to reduce a program quantity, to reduce a burden applied to a CPU, and to execute an operation with a high efficiency by providing a chatter eliminating circuit and an effective level detecting circuit on all of plural input ports. CONSTITUTION:When a level variation from the outside appears in an input terminal P1 of an input port L1, F1 and F2 of an FF are operated by the first and the second clocks PHI1, PHI2 in four pieces of scan clocks, in order to discriminate whether its level variation is an effective variation or a chatter which becomes a fault. In case of a different state of the input terminal P1 has been sampled at two points of the fall of the clocks PHI1, PHI2, the output of an exclusive NOR gate E1 becomes '0', it is regarded as a chatter signal, and it is not executed to set the input port L1 to a register F3. Also, in case of P1 potential has sampled the same state at two points of a fall of the clocks PHI1, PHI2, the output of the NOR gate E1 becomes '1', its value is regarded as an effective level, and its state value is set to the register F3 at a rise of a scan clock PHI3.
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