Publisher Summary Everything that users need to know is provided in data sheets that are freely available from manufacturers, suppliers, or in many electronic catalogs. A data sheet is not the most exciting reading that is available, but like a telephone directory, it can be very useful. The supply voltage should be used if the performance and reliability is to be guaranteed. High-level input voltage (VIH) is the lowest voltage that the gate accepts as logic 1 level. It sometimes varies according to the supply voltage. Supply current is the current that is needed to work the internal circuit. Output current is a question of how much current the gate can supply to another circuit. It controls an output display or the other gates. The value of this current may differ according to the logic state of the output. Some gates can provide a higher current when the output is at logic 0 than when it is at logic 1, whereas the current levels are the same in many of the more modern gates.