| 摘要 |
PURPOSE:To discriminate the state of logical values 1, 0 and a high impedance with one external terminal, by constituting a circuit detecting the logical values of the external terminal and a circuit detecting the high impedance state of the external terminal on a same substrate. CONSTITUTION:An external terminal T is connected to an input section U1 in a logical integrated circuit. The input section U1 consists of a circuit U11 discriminating logical values 1, 0 and a circuit U12 discriminating the high impedance state. A voltage and a ground potential are connected to the terminal T via switches SWS1, S2. When the SWS1 is turned on and the SWS2 is turned off, the circuit U11 detects the logical value 1 at the terminal T and when the SWS1 is turned off and the SWS2 is turned on, the circuit U11 detects the logical value 0. When both switches SWS1, S2 are turned on, the circuit 12 detects the high impedance state at the terminal T. Thus, the tri-state of the external terminal is discriminated with the method of external terminal control simply, allowing to attain the external terminal effectively. |
