identical and will not be discussed input buffer 10 must discriminate among voltage levels on busin 12 to determine whether a logic 1 or logic 0 is present any voltage below 0 8 volts will be interpreted by input buffer 10 as a logic 0 and anything above 2 0 volts will be deemed a logic 1 when the supply voltage vcc is equal to 5 0 volts input circuit 14 is utilized to detect whether a logic or 0 is present input circuit 14 as shown in fig1 is a schmidt trigger inverter configuration it should be understood that other input circuit configurations such as a simple inverter having a trip level at 0 28 vcc may be utilized input circuit 14 sets the trip level of input buffer 10 to about 1 4 volts thus any voltage higher than 1 4 volts entering busin input 12 will be output by input circuit 14 at input circuit 14 output node 18 as a logic signal likewise any voltage on busin input 12 detected by input circuit 14 being less than 1 4 volts will cause an output on input circuit 14 output node 18 of a logic 0 for an operating system of 3 3 volts however input circuit 14 is ineffective since the trip point lowers to about 0 84 volts because of the reduced supply voltage such a trip point is too low to detect a logic 1 or 0 correctly because of temperature and integrated circuit process variations there is a danger that a voltage of 0 8 volts or.