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Combinational logic is used to build circuits that produce specified outputs from certain inputs. The construction of combinational logic is generally done using one of two methods: a sum of products, or a product of sums. Consider the following truth table:
The Boolean logic for the sum (in this case ) will be whereas for the carry will be . With the addition of an OR gate to combine their carry outputs, two half adders can be combined to make a full adder. [2] The truth table for the half adder is:
Switching circuit theory is the mathematical study of the properties of networks of idealized switches. Such networks may be strictly combinational logic, in which their output state is only a function of the present state of their inputs; or may also contain sequential elements, where the present state depends on the present state and past states; in that sense, sequential circuits are said ...
This explains why "EQ" is often called "XNOR" in the combinational logic of circuit engineers, since it is the negation of the XOR operation; "NXOR" is a less commonly used alternative. [1] Another rationalization of the admittedly circuitous name "XNOR" is that one begins with the "both false" operator NOR and then adds the eXception "or both ...
Figure 1: Logic diagram for a half subtractor. The half subtractors can be designed through the combinational Boolean logic circuits [2] as shown in Figure 1 and 2. The half subtractor is a combinational circuit which is used to perform subtraction of two bits.
PLA schematic example. A programmable logic array (PLA) is a kind of programmable logic device used to implement combinational logic circuits.The PLA has a set of programmable AND gate planes, which link to a set of programmable OR gate planes, which can then be conditionally complemented to produce an output.
Several important complexity measures can be defined on Boolean circuits, including circuit depth, circuit size, and the number of alternations between AND gates and OR gates. For example, the size complexity of a Boolean circuit is the number of gates in the circuit. There is a natural connection between circuit size complexity and time ...
A truth table is a mathematical table used in logic—specifically in connection with Boolean algebra, Boolean functions, and propositional calculus—which sets out the functional values of logical expressions on each of their functional arguments, that is, for each combination of values taken by their logical variables. [1]