Sequential logic circuits, what sequential logic circuits are made of

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).

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. It is different from other circuits that we are familiar with, its output state at any moment is determined by the input signal at that time and the original state of the circuit, and its state is mainly memorized and represented by the memory circuit. At the same time, the particularity of the structure and function of sequential logic circuits is often difficult, complex and wide range of applications compared with other types of digital logic circuits.

In the digital circuit is usually divided into two categories: combinatorial logic circuit and sequential logic circuit, the relevant content of combinatorial logic circuit has been introduced in the previous chapter, the characteristic of combinatorial logic circuit is that the change of input directly reflects the change of output, the state of its output only depends on the current state of the input, and has nothing to do with the original state of input and output, and the sequential circuit is an output not only related to the current input, but also related to the original state of its output state, It is equivalent to adding a feedback input to the input of the combinatorial logic, and there is a memory circuit in the circuit, which can maintain the state of the output, and we can use the block diagram in the following figure to describe the composition of the sequential circuit.

As can be seen from the above figure, its output is a function of the state of the input and output at the previous time, and then the output function expression cannot be represented by the method of combining the function expression of the logic circuit, and the concepts of present state and next state are introduced, when the present state represents the current state (usually represented by qn), and the secondary state represents the state of its output after the input changes (usually represented by qn 1), Then the output state after the input change is expressed as.

qn 1=f(x,qn)

where x is the input variable.

Looking at the landlord's question, it should be the digital logic circuit that should be learned, which is mainly divided into sequential logic circuit and combined logic circuit.

Sequential logic circuits are understood by definition to mean that the output depends on the current input and the previous output, and generally has a memory structure to store the previous output, and then the previous output and the current input together determine the output this time. The output of a combinatorial logic circuit depends only on the current input.

In fact, when the logic circuit is combined, there is no clock, and the sequence circuit has a clock, and the combination logic circuit can think that when the signal comes, the output will then change; A change in the input of a timing circuit does not immediately cause an output change, but rather an output change every time the clock is taken.

There is really no good way to learn to count electricity, but the landlord watched it quietly for two days, understood, and got started, so it was easy to learn.

Let's explain it this way first, and then add if the landlord has any questions.

High school physics.

NAND Gate. or doors.

NAND gate is a logic circuit that is connected with 1 and not at all. The output result of the NAND gate is exactly the opposite of the input, e.g. the input has a signal but the output is 0 (no signal), and there is no input signal but the output is 1 (there is a signal connected). NAND gate is a combination of gate and NAND gate, performing AND operations first, and then non-operations.

If both inputs are represented by 0 and 1, then the result of the AND operation is the product of these two numbers. If 1 and 1 (there are signals at both ends), the output is 1; 1 and 0, the output is 0; 0 and 0, this output is 0. The result of the NAND gate is the result of performing an AND operation on two input signals and then a non-operation on the result.

To put it simply, non-and non-is the first and the last.

If you don't understand it yet, I'll go and review it and tell you.

It consists of two parts: a storage circuit (various triggers) and a combined logic circuit.

The output of a sequential logic circuit at any given moment depends not only on the input at that moment, but also on the input at each moment in the past. Common sequential logic circuits include flip-flops, counters, registers, etc. Because sequential logic circuits have the function of storing or memorizing, they are more complicated to overhaul.

The clock is the synchronization signal of the whole system, and when the clock fails, it will bring about the overall functional failure. Clock pulse loss causes the system data bus, address bus, or control bus to become inactive. Changes in the rate, amplitude, width, shape, and phase of a clock pulse can cause failures.

It consists of two parts: a storage circuit (various triggers) and a combined logic circuit.

The output of the circuit is not only related to the input, but also to the original state of the circuit at that moment

What is a Sequential Logic Circuit: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.

The combinatorial logic circuit is that the output at any time depends only on the input at that time, and has nothing to do with the original state of the electrokinetic infiltration path. 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, but sequential logic kernel 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.

Sequential logic circuits are divided into: synchronous sequential circuits and asynchronous sequential circuits.

Synchronous sequential circuitryThe input of the synchronous timing circuit is the clock, and the timing and delay of the circuit are controlled. Therefore, the synchronous timing circuit can be further divided into: clock synchronization timing circuit and pulse synchronization timing circuit.

The schematic diagram is as follows:

Asynchronous sequential circuitryAsynchronous sequential circuits are characterized by the fact that there is no uniform clock to control the switching of circuit states. The input data will directly affect the change of the circuit shape. then cavity.

Example of a counter for an asynchronous spine timing circuit (note how the clock is connected) Sun Heshan: