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VOOZH | about |
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VOOZH | about |
Sequential circuits are digital circuits that store and use previous state information to determine their next state. They are commonly used in digital systems to implement state machines, timers, counters, and memory elements and are essential components in digital systems design.
Sequential circuit is a combinational logic circuit that consists of inputs variable (X), logic gates (Computational circuit), and output variable (Z).
A combinational circuit produces an output based on input variables only, but a sequential circuit produces an output based on current input and previous output variables. That means sequential circuits include memory elements that are capable of storing binary information. That binary information defines the state of the sequential circuit at that time. A latch capable of storing one bit of information.
As shown in the figure, there are two types of input to the combinational logic :
Secondary inputs are state variables produced by the storage elements, whereas secondary outputs are excitations for the storage elements.
There are two types of sequential circuits
These circuits do not use a clock signal but uses the pulses of the inputs. These circuits are faster than synchronous sequential circuits because there is clock pulse and change their state immediately when there is a change in the input signal. We use asynchronous sequential circuits when speed of operation is important and independent of internal clock pulse.
But these circuits are more difficult to design and their output is uncertain.
These circuits uses clock signal and level inputs (or pulsed) (with restrictions on pulse width and circuit propagation). The output pulse is the same duration as the clock pulse for the clocked sequential circuits. Since they wait for the next clock pulse to arrive to perform the next operation, so these circuits are bit slower compared to asynchronous. Level output changes state at the start of an input pulse and remains in that until the next input or clock pulse.
We use synchronous sequential circuit in synchronous counters, flip flops, and in the design of MOORE-MEALY state management machines. We use sequential circuits to design Counters, Registers, RAM, MOORE/MEALY Machine and other state retaining machines.
Clock signal is a kind of control signal that allows the elements of synchronous circuits to be in phase or phenomena that occur in circuits. It is derived from the square wave that has a high and a low level, it helps in measuring the sequential changes in the circuit states. The clock signal also makes a pulse simultaneously on all the circuit parts that are needed for the proper work of synchronous sequential circuits.
In Sequential circuits, triggering denotes the way, in terms of which the state changes take place. There are two main types of triggering
Level triggering happens when the change of state is from the level of the clock signal is high or low. The circuit depends on the level of the clock signal rather than the rising or the falling edge of it. There are two types of level triggering:
Edge triggering occurs when the state change is initiated by the transition (rising or falling edge) of the clock signal. The circuit responds to the clock signal's edges rather than its levels. There are two types of edge triggering:
Sequential circuits find application in virtually almost every digital system today because of their capacity to handle state information. Some common applications include:
