How does CRC work?

Chapter 1  Introduction

Chapter 1.1 Introduction
Everyone has encountered the message “CRC data error… and something else” at some point. This is an error that appears, for example, when transmitting data from a CD to a hard drive, or more generally – when exchanging data between two devices in the network. I hope that after this course you will know what I mean.

Chapter 1. 2 Very important!!! How to enter and exit each animation
The main advantage of this coursel is animation, which makes it easier to understand the topic. You activate it by clicking the word ANIMATION. located under most drawings. You then enter the appropriate page of the SCRATCH program server, but at the same time you exit this portal page! Therefore, when everything is clear, go back by clicking the classic Windows “return to previous page” arrow button.
And one more thing. Don’t click the clock too fast! The system can get confused.

Fig. 1-1

How to return from animation to the course.

Chapter 1. 3 Transmission without CRC
That is, without error checking. The topic is so obvious that consider it more of an opportunity to learn about animation. Click ANIMATION under Fig.1-2. You will perform experiments in the same way later in the course.
Fig. 1-2
Transmission without CRC ANIMATION
The AIR Transmitter (Register of Appropriate Information) is e.g. in London and the RR in New York. Each clock pulse “pushes” one byte with the do number from the AIR to the RR. This is, of course, a simplification, because each byte is converted into an appropriate sequence of bits.
An explanation bubble appears in each system state.

Chapter. 1. 4 Transmission with CRC
That is, with error checking. There may be interference on the cables between the Transmitter and the Receiver from various sources, e.g. from electromagnetic waves. Then the RR state will be, for example, RR=38547 instead of 32547. We are so smart because in the animation we see AIR in London and RR in New York at the same time. But how is that poor AIR in London supposed to know about this? You will learn about this in the next chapter. You will also learn why the register in the Transmitter is called AIR-Register of Proper Information and not simply TR-Transmitter Register.

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