Edge-triggered Flip Flops. Flip Flop. Flip flop timing. Slave Hold Time. Dynamic Discipline. N-bit Register. Adding logic to clocked devices. Finite State Machine. Single Clock Synchronous Discipline. Single Clock Synchronous System. Synchronous Hierarchy. Example: Sequential Circuit Timing. Clocked device example. RAM Arrays. A latch capable of storing one bit of information. Skip to content. Change Language. Related Articles. Introduction of Boolean Algebra and Logic Gates.
Combinational Circuits. It has two stable states, but one stable state at a time, and the stable output state is concerning the input. When a noise as a voltage or other form adds up to the output, which can make the circuitry unstable, and the output may not be stable at a definite state, but as the noise crosses through either of the inverters, it gets eliminated as this circuit is regenerating always trying to return to a definite stable state, which helps us to create an active and regenerative memory cell.
The above diagram is the CMOS circuit is of the memory cell two inverters connected in the feedback. With the finite number of inputs and outputs, the sequential logic circuit is used to construct a finite state machine. It can act as a register, counter, etc. With the help of a combinational circuit, many basic devices can be created like RAM Random Access Memory , as sequential logic circuit provides us with the facility to store data it opens the door to the microprocessor and Arithmetic logic Circuit.
The output of a sequential logic device can be manipulated by the current input and by the previous input or clock pulses. Sequential devices store the last data with a memory element. With this capability of storing data these devices, open new ways to solve a problem.
A significant advantage of sequential logic is that its circuit contains a memory element that enables storing data and creating a register, counter, and microprocessors.
With the use of clock pulse, it can synchronize all the circuitry elements regardless of different propagation delays and provide proper output. Output can be manipulated through current input, past sequence of inputs, and through clock pulse also. Presence of a clock and feedback in the circuitry, the processing of the output can be slower. Complications of the circuit may increase, which can cause difficulty in building the circuitry.
The output is sometimes can be uncertain. Sequential logic is utilized for the development of finite state machine, which is a basic building block of all digital circuitry. For more information click here.
The encoder is a combinational circuit that mainly converts one form of data to another format, such as decimal data to binary data. The decoder here is also a combinational circuit. The same goes for Multiplexer, Adder, and Subtractor. All are here is a combinational circuit. In ROM, we cannot alter the content of the memory.
Therefore the output of the ROM is only dependent on the input. So there is no requirement of the past value of input or output. So, ROM has only a combinational circuit in its circuitry. In the case of PROM, it can be programmed once after manufactured. In this type of memory, we always need the sequential circuit for proper operation, as here, there is a need for past input and output values.
Generally, we come across many counters in our daily life to count the number of objects. For example to count the number of audience entering or leaving an auditorium or to count number of vehicles in parking. In this when any person enters in to auditorium the counter increments its value depending on its present value. Similarly, it decrements its value depending on its previous and present value. So Counter retains the present state of the counter to do next operation. This is analogous to sequential circuits which changes their state according to the previous and present signals.
Back to top. Combinational Circuits Sequential Circuits Output depends only on the present value of the inputs. Output depends on both the present and previous state values of the inputs These circuits will not have any memory as their outputs change with the change in the input value.
Sequential circuits have some sort of memory as their output changes according to the previous and present values. There are no feedbacks involved. In a sequential circuit the outputs are connected to it as a feedback path.
Used in basic Boolean operations. Used in the designing of memory devices. Implemented in: Half adder circuit, full adder circuit, multiplexers, demultiplexers, decoders and encoders. Implemented in: RAM, Registers, counters and other state retaining machines.
The clock signal plays a crucial role in sequential circuits. A clock is a signal, which oscillates between logic level 0 and logic level 1, repeatedly. Square wave with constant frequency is the most common form of clock signal. These are the instants at which the clock changes from 0 to 1 a positive edge or from 1 to 0 a negative edge. Clock signals control the outputs of the sequential circuit. That is it determines when and how the memory elements change their outputs.
If a sequential circuit is not having any clock signal as input, the output of the circuit will change randomly. So that they cannot retain their state till the next input signal arrives. But sequential circuits with clock input will retain its state till the next clock edge occurs. Classification of Sequential Circuits Based on the clock signal input, the sequential circuits are classified into two types.
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