| 摘要 |
PURPOSE:To set the best input threshold according to an external circuit which is connected by providing a threshold value switching circuit which switches threshold values of an input stage circuit which receives an external signal stepwise with a control signal. CONSTITUTION:Inverters INV1 and INV2 of the input stage circuit has threshold values VT1 and VT2 and both input a signal from a terminal 2. When the control signal TL is at a level L, an NAND gate ND1 is closed, an NAND gate ND2 is opened by the inverter IN3, and the output of the INV2 is used to obtain the effective threshold value VT2 of the input circuit 1, which is outputted from an NAND gate ND3. In this state, this is used when a TTL-level signal is inputted. When a signal CTL is at a level H, the gate ND2 is closed and the gate ND1 is opened to use the output of the INV1, so that the effective vaule of the circuit 1 is VT1. In this state, this is used when a CMOS-level signal is inputted. |
