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Sequential logic circuits are generally termed as two state or bistable devices which can have their output or outputs set in one of two basic states, a logic level “1” or a logic level “0” and will remain “latched” indefinitely in this current state or condition until some other input trigger pulse or signal is applied which will cause the bistable to change its state once again.

Sequential Logic circuits remember these conditions and stay fixed in their current state until the next clock signal changes one of the states, giving sequential logic circuits “Memory”. In other words, the output state of a “sequential logic circuit” is a function of the following three states, the “present input”, the “past input” and/or the “past output”. Unlike combinational logic circuits whose output depends upon the signals being applied to the inputs at that time, Sequential Logic circuits have some form of memory built in to them so that they are able to take into account their previous input state as well as those at present. Logic Diagram: This is a graphical representation of a logic circuit that shows the wiring and connections of each individual logic gate, represented by a specific graphical symbol, that implements the logic circuit.Ĭlassification of Combinational Logic Circuits.Truth Table: A truth table defines the function of a logic gate by providing a concise list that shows all the output states in tabular form for each possible combination of input variable that the gate could encounter.Boolean Algebra: This forms the algebraic expression showing the operation of the logic circuit for each input variable either True or False that results in a logic “1” output.The three main ways of specifying the function of a combinational logic circuit are: These logic gates are the building blocks of Combinational Logic Circuits.Ĭombinational logic circuits can be very simple or very complicated and any combinational circuit can be implemented with only NAND and NOR gates as these are classed as universal gates. Combinational Logic Circuits are made up from basic logic gates such as NAND, NOR or NOR gates that are combined or connected together to produce more complicated switching circuits.