There is a risky phenomenon in the circuit of the combinatorial logic circuit design, and what measu

The phenomenon of transient errors in the output of the circuit due to competition is called risk-taking. It is manifested as a narrow pulse at the output that was not present in the original design, and is often referred to as a glitch.

Judge a logic circuit.

Whether there will be a risk when some input signals change, first of all, we must judge whether the signals will change at the same time, and then determine whether there will be a risk when the signals change at the same time, which can be done through the Carnot diagram of the logic function.

or logical function expressions.

to judge.

The phenomenon of risk-taking is due to digital circuits.

False digital signals caused by internal design or external influences.

adverse effects. In a digital circuit, the input digital signal changes or performs some logic operations.

If not, with, or, etc.), the output signal is not completely synchronized, resulting in a short period of false signal pulse output.

When there is a risk-taking phenomenon in the combined logic circuit, various methods can be adopted to eliminate the risk-taking phenomenon, such as modifying the logic design, adding a gating circuit, and increasing output filtering.

In terms of the specific causes that cause adventure, adventure can be divided into functional adventure and logical adventure. Functional risk-taking is inherent in logical functions themselves, and often occurs when multiple input variables change. The easiest way to avoid the risk of a function is to allow only a single input variable to change at a time, or to take samples.

When a single input variable changes, there is no functional adventure, but when the circuit design is not suitable, there is still a logical adventure. With careful design, the structure of the circuit can be modified, and the logic adventure can be eliminated.

<>1. Characteristics of combined logic circuits:

Combined logic circuits are referred to as combined circuits, and the characteristics of logic function are 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. The logic function of a sequential logic circuit is characterized by the fact 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, on the previous input.

2. Digital circuits can be divided into two categories according to the different characteristics of logic functions, one is called combined logic circuits, referred to as combined circuits, and the other is called sequential logic circuits, referred to as sequential circuits.

The reason for the competitive adventure: due to the existence of delay time, when an input signal is transmitted through multiple paths and then rejoins to a certain door, due to the different stages of different paths to the door, or the difference in the delay time of the gate circuit, the time to reach the meeting point is first and last, resulting in instantaneous error output.

1. Reasons for competition:

In a combinatorial logic circuit, an input variable is transmitted to the output through two or more paths, and the time to reach the output gate is first and second due to the different delay time of each path, which is called competition. The phenomenon of competition, which does not produce false output, is called noncritical competition. The phenomenon of competition, which produces temporary or permanent erroneous outputs, is called critical competition.

2. Reasons for taking risks:

There is a certain delay as the signal passes through the wires and logic units inside the device. The size of the delay is related to the length of the connection and the number of logic units, and is also affected by the manufacturing process of the device, operating voltage, temperature, and other conditions. The transition time between high and low levels of the signal also occurs.

Due to the existence of these two factors, when the level value of the multi-channel signal changes, at the moment of signal change, the output of the combinatorial logic has a sequential order, and does not change at the same time, and some incorrect spike signals often appear, which are called spike signals"Burrs"。If there is a combinatorial logic circuit"Burrs"appears, indicating that there is a risk in the circuit.

There are 5 representations of combinatorial logic circuits, which are;

1. Logical prudence function notation.

2. Logic circuit notation (logic algebra). God accompanies you.

3. Truth table notation.

4. Carnot diagram notation.

5. Logic waveform table width blind punching method.

It's best to master all of these methods and transform them into each other.

The design steps of a combinatorial logic circuit are as follows: determining the logic function, determining the input and output, designing the logic expression, determining the gate type, and combining the circuit.

1. Determine the logic function: Determine the logic function that the circuit needs to achieve according to the actual needs, such as addition, subtraction, comparison, selection, etc.

2. Determine the input and output: determine the input and output ports of the circuit, as well as the data type and format of the input and output.

3. Design logical expressions: According to the logic function, design the logical expressions of the circuit, such as Boolean algebra formulas, Carnot diagrams, etc.

4. Determine the type of gate circuit: According to the logical expression, determine the type of gate circuit, such as AND door, or door, non-gate Wang Limb Zen, etc.

5. Combined circuit: according to the logic expression and gate circuit type, the combination circuit realizes the logic function.

a.Write a Logos Cave Slide expression.

b.Express the dry style to make the light simpler.

c.Column truth table.

d.Draw a logical diagram.

Correct answer: c

The main steps of combinatorial logic circuit design are briefly described as follows:

1) List the truth table from the actual logic problem;

2) Write a logical expression from the truth table;

3) Simplifying and transforming the output logical expression;

4) Draw a logic diagram.

and logical representation that the result occurs only when all the conditions that determine the outcome of a thing are met. The combination of all factors of a combination with an output variable of 1 and the combination of all factors representing an output variable of 1 and all combinations of output variables of 0 do not appear, so that a combination with an output variable of 1 can be described.

The analysis of a combinatorial logic circuit is carried out in the following steps:

1) Have a given logic circuit diagram and write the logical expression of the output;

2) List the truth table;

3) Summarize the logic function of Hu hail through the truth table to see if the original circuit is the best, if not, improve it.

Common arithmetic operation circuits are:

1. Half adder and full adder.

Semi-adder. Add the two numbers A and B, only find the sum of the standard, and ignore the carry number sent by the low position for the time being, which is called "half addition".

The circle that completes the half-plus function is called a half-adder. In actual binary addition, the two additions are generally not one, so a half-adder that does not take into account the low carry will not solve the problem.

Full adder. The addition of two numbers, considering not only the sum of the bases, but also the number of carry digits from the lower digits, is called "full addition". The logic circuit that implements this function is called a full adder.

2. an adder.

A circuit that implements the addition of multi-bit binary numbers is called an adder. According to different carry methods, there are two kinds of serial carry adders and super-forward adders.

Four-bit serial adder: e.g. T692. Pros:

The circuit is simple and easy to connect. Disadvantages: The computing speed is not high.

The calculation of the highest bit must wait until all the low bits are completed and the carry signal is sent. In order to improve the computing speed, the super-forward mode can be used.

Super-forward adder: The so-called super-forward is that when doing addition operations, the carry signal of the digits is directly generated by the input binary number.