12/10/2023 0 Comments Sequential logic circuitTherefore, the "modulo" of the counter is actually the number of valid states of the circuit. Such as M=6 counter, also known as hexadecimal counter. The maximum number of accumulated input pulses of the counter is called the "modulo" of the counter, which is denoted by M. The output of the counter is usually a function of the current state. Generally speaking, the counter is mainly composed of triggers, used to count the number of input count pulse CP. In the specific lectures, three logic devices with wide application and typical sequential logic circuit characteristics are selected for detailed introduction. Sequential logic circuits are widely used, and are divided according to the different logic functions required, and there are many types. All the circuits in Figure a are called latches, and the circuits shown in Figure b are called flip-flop circuits.įeatures of sequential logic circuits: The output at any time depends not only on the input at that time, but also on the original state of the circuit, so the sequential circuit has a memory function. The difference between the two is whether their output state changes depend on CP (clock pulse clock) Pulse). Generally, the above two types are divided into two forms of memory circuits: latches and flip-flops. Only when the CP is high, the state of the input can affect the state of the output. It can be seen from the figure a above that there are four cases where the input RS is 0, but the state of its output Q is different, which depends on the original state of the output and the input in the figure b is the same as the figure a, But there is one more CP, then the output Q depends not only on the original state of the input RS and output Q, but also on the state of the CP. The following uses two waveforms to help establish the concept of memory in sequential circuits: The concepts of Present state and Next State, when the present state represents the current state (usually represented by Qn), and the second 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 At this time, the output function expression cannot be expressed by the function expression method of the combinational logic circuit. It can be seen from the above figure that the output is a function of the state of the input and the time before the output. We can use the block diagram below to describe the composition of the sequential circuit. The state of the output depends only on the current state of the input, and has nothing to do with the original state of the input and output, and the sequential circuit is a kind of output not only related to the current input, but also related to the original state of its output state, which is equivalent to the combinational logic A feedback input is added to the input end of the, and there is a storage circuit in its circuit, which can maintain the state of the output. The characteristic of combinational logic circuits is that changes in input directly reflect changes in output. The relevant contents of combinational logic circuits have been introduced in the previous chapters. At the same time, the particularity of the structure and function of sequential logic circuits is often more difficult, complicated and has a wide range of applications compared to other types of digital logic circuits.ĭigital circuits are usually divided into two categories: combinational logic circuits and sequential logic circuits. 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 expressed by the storage circuit. It is different from other circuits we are familiar with. Sequential logic circuits, also known as sequential circuits, are mainly composed of memory circuits and combinational logic circuits. Sequential logic circuits are an important part of digital logic circuits.
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