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Figure 17 lists basic details of the six most popular OR gate ICs: Simple three input diode OR gate.
Ways of cascading two-input OR gates to get up to five inputs. Relatively few dedicated OR gate ICs are available.
IC 74HC TTL Quad 2−Input NAND Gate with Schmitt−Trigger
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 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. Part 4 Practical digital mixed gate and special-purpose logic gate ICs such as programmable logic, majority logic, and digital transmission gate types.
The output of an OR gate goes high when any of its inputs A or B, etc. 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. Six popular OR gate ICs.
The diode OR gate is reasonably fast, very cost-effective, and can if be expanded to accept any number of inputs by simply adding one more diode to the circuit for each new input. Also note that OR gates can be directly cascaded to make a compound OR gate with any desired number of inputs.
Need to brush up on your electronics principles? Just make sure the buffer has a fan-in of one in the former case, and a fan-in of two in the latter.
Understanding Digital Buffer, Gate, and Logic IC Circuits – Part 3
These multi-part series may be just what you need! Example of a compound five-input OR gate circuit.
The 74LS10 and B see Figures 6 and 7 are triple three-input standard types; the 74LS20 and B see Figures 8 and 9 are 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. Learning Electronics Need to brush up on your electronics principles?
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 74jc132 both inputs together, as shown in Figure