The output of an OR gate goes high 74hc123 any of its inputs A or B, etc. Learning Electronics Need to brush up on your electronics principles? These multi-part series may be just what you need! Part 4 Practical digital mixed gate and special-purpose logic gate ICs such as programmable logic, majority logic, and digital transmission gate types.
Example of a compound five-input OR gate circuit. Need to brush up on your electronics principles? The 74LS10 and B see Figures 6 and 7 are triple three-input standard types; the 74LS20 and B see Figures 8 and 9 lc dual four-input standard types; the 74LS30 and B see Figures 10 and 11 are eight-input standard types; and the 74HC is a input standard type.
Understanding Digital Buffer, Gate, and Logic IC Circuits – Part 3 | Nuts & Volts Magazine
In this case, the unwanted inputs can be disabled by either tying them high directly in CMOS gates, or via a 1K resistor in TTL types or by simply shorting them directly to a used input. Note that the fan-in of a TTL NOR gate is directly proportional to the number of inputs used — at a fan-in rate of one per input — and that a TTL two-input OR gate can be made to act as a simple non-inverting buffer by either tying one input to ground or by tying both inputs together, as shown in Figure Figure 24for example, shows ways of cascading two-input elements to make OR gates with three, four, or five inputs, and Figure 25 shows a three-input OR element and a three-input diode OR gate cascaded to make a compound five-input OR gate.
Relatively few dedicated OR gate ICs are available. Just make sure the buffer has a fan-in of one in the former case, and a fan-in of two in the latter. The simplest way to make an OR gate is via a number of diodes and a single resistor, as shown for example in the three-input OR gate of Figure Ways of cascading two-input OR gates to get up to five inputs.