What is the difference between combinatorial logic circuits and sequential logic circuits in terms o

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The output of a combinatorial logic circuit is only related to the input, and the output of a sequential logic circuit is not only related to the input but also to the initial state.

Their logic functions and circuit structures are analyzed on a case-by-case basis, but they are obviously related to the initial state that are implemented by sequential logic circuits. In many cases, the two are combined.

Since the output of the sequential logic circuit is not only related to the current input, but also related to the current state of the circuit, in the circuit structure, the sequential logic circuit will contain memory devices, such as flip-flops, registers, etc., which are used to save the state of the circuit.

1. Features.

1. The characteristic of the logic function of the combined logic circuit is that the output at any time only depends on the input at that time, and has nothing to do with the original state of the circuit.

2. The characteristics of the sequential logic circuit in the logic function are that the output at any time depends not only on the input signal at that time, but also on the original state of the circuit, or in other words, it is also related to the previous input.

Second, the analysis methods are different.

1. The analysis steps of the combined circuit are roughly as follows:

1) According to the given logic circuit diagram, write the logical expression of each output;

2) simplifying and transforming each logical expression;

3) Make a list of truth values;

4) A review of the logical function.

2. General analysis methods of sequential logic circuits.

1) Driving equation: according to the analysis method of the combined logic circuit, write the logical relationship of the trigger input;

2) Equation of state: analyze the logical relationship between the input and the output of the trigger (the state of the trigger) according to the characteristic table or characteristic equation of the trigger;

3) Output equation: according to the analysis method of the combined logic circuit, the combined logical relationship between the output of the flip-flop (the state of the flip-flop) and the output of the sequential logic circuit is expressed;

Third, it depends on the state of the difference.

1. A combinatorial logic circuit means that the output state at a certain moment only depends on the input state at that time, and has nothing to do with the past state of the circuit.

2. The characteristics of the sequential logic circuit in the logic function are that the output at any time depends not only on the input signal at that time, but also on the original state of the circuit, or in other words, it is also related to the previous input.

Sequential logic circuits contain memory cells, and the outputs are not only related to the input, but also to the previous state, and combinatorial logic circuits do not contain memory cells, and the outputs are related to the inputs, not to the previous state.

A combinatorial logic circuit is one in which the output is only related to the current input, whereas the output of a sequential logic circuit is related not only to the current input but also to the previous state of the circuit. In other words, sequential logic circuits have elements that have memory functions, such as various flip-flops.

The difference between combinatorial logic circuit and sequential logic circuit is reflected in the input-output relationship, whether there is a memory (memory) unit, and the structural characteristics.

1. Input-output relationship.

A combinatorial logic circuit is one in which the output at any moment in time depends only on the input at that moment, regardless of the original state of the circuit. Sequential logic circuits depend not only on the current input signal, but also on the original state of the circuit, or in other words, on previous inputs.

2. Whether there is a storage (memory) unit.

Combinatorial logic circuits do not have memory memory, while sequential logic circuits do.

3. Structural characteristics.

The combinatorial logic circuit only contains the circuit, but the sequential logic circuit contains the combinatorial logic circuit + storage circuit, and the output state must be fed back to the input end of the combinatorial circuit, and the output of the combinatorial logic is determined together with the input signal.

First, the nature is different.

1. The nature of the combined logic circuit: at any time, the output state is only determined by the combination of the input states at the same time, and has nothing to do with the previous state of the circuit, but has nothing to do with the state of other times.

2. Sequential logic circuit properties: an important part of digital logic circuits.

Second, the characteristics are different.

1. Characteristics of combined logic circuit: the output at any time only depends on the input at that time, and has nothing to do with the original state of the circuit.

2. Characteristics of sequential logic circuit: the output at any time not only depends on the input signal at that time, but also depends on the original state of the circuit, or in other words, it is also related to the previous input.

Third, the principle is different.

1. Principle of combinatorial logic circuit: In the actual design work, if some gate circuits cannot be obtained for some reason, the circuit can be changed by changing the logic expression, so that other devices can be used to replace the devices. At the same time, in order to make the design of logic circuits more concise, it is necessary to simplify the logic expressions through various methods.

2. The principle of sequential logic circuit: its state is mainly stored and represented by the memory circuit. The output is not only related to the current input, but also to the original state of the output state.

It is equivalent to adding a feedback input to the input of the combinatorial logic. There is a memory circuit in the circuit that keeps the output in its state.

The timing circuit has a memory function. Sequential circuits are characterized by the fact that the output depends not only on the input value at the time, but also on the past state of the circuit.

The logic function of a combinatorial logic circuit is characterized by the fact that the output at any moment only depends on the input at that time, regardless of the original state of the circuit.

The differences between combinatorial logic circuits and sequential logic circuits are briefly described as follows:

Sequential logic circuits have memory functions, and sequential circuits are characterized by the following: the output not only depends on the input value at that time, but also is related to the past state of the circuit; The characteristics of the logic function of the combinatorial logic circuit are that the output of the squire at any time only depends on the input at that time, and has nothing to do with the state of the circuit.

According to the different characteristics of logic functions, digital circuits can be divided into two categories, one is called combined logic circuits (referred to as combined circuits), and the other is called sequential logic circuits (referred to as sequential circuits).

From the perspective of **, the timing logic is a sensitive list with a rising edge of the clock, if there is no rising edge or a ** with a "*" sign, it is a combination logic. At the circuit level, the circuits reflected by the two types of logic are also different, and the sequential logic is equivalent to an additional D flip-flop on the basis of the combined logic.

At the waveform diagram level, the waveform of the combinatorial logic reflects the change immediately and has nothing to do with the clock. However, the waveform of the timing logic is not reflected immediately, only the rising edge of the clock.

Introduction to Combinatorial Logic Circuits and Sequential Logic Circuits:

1. Combined logic circuit.

A combinatorial logic circuit is a combination of output states that determine only the input states at the same time at any time, regardless of the previous state of the circuit, and not the states of other times. Commonly used combinatorial logic circuits include arithmetic operation circuits, encoders, decoders, data selectors, data distributors, etc.

In order to make the design of logic circuits more concise, it is necessary to simplify the logic expressions by various methods. On the basis of satisfying the logic function and technical requirements, it is required to make the circuit simple, economical, reliable, and the way to realize the combined logic function is a variety of leads, which can use basic gate circuits, medium and large-scale integrated circuits.

2. Sequential logic circuit.

Sequential logic circuit is an important part of digital logic circuit, which is mainly composed of two parts: storage circuit and combined logic circuit. The characteristics of the sequential logic circuit in the logic function are that the output at any time depends not only on the input signal at that time, but also on the original state of the circuit, so the sequential logic circuit has a memory function.

Sequential logic circuit is an important part of digital logic circuit, sequential logic circuit, also known as sequential circuit, which is mainly composed of two parts: storage circuit and combined logic circuit.