Communication

1. About communication

Communication is when two or more objects are connected to transmit or receive information. There are many types of communication methods depending on the distance to opponent or the environment. Before knowing the communication itself, it is necessary to understand the criteria for communication selection. Let's take a look at some of the characteristics below.

 

2. Communication characteristics – Serial and parallel

p class=MsoNormal style='margin-bottom:0cm;text-indent:10.0pt;line-height: normal'>If there are 8 data, the simplest way to finish communication is to make 8 lines between the transmitter(TX) and the receiver(RX) and send them all at the same time. Parallel communication that sends multiple data at once will end very quickly, but other problems that arise are not simple. The number of data changes for each content to be communicated, so it is impossible to send one data per line every time, and there are limits to the cost and space to create a line.
  If so, let's reduce the number of lines to a minimum to reduce the cost and transmit all 8 data on one line. In the case of this serial communication, it will take a long time to communicate, but even if there is more data, it is solved by transmitting all of it on the same line. However, since the receiver cannot distinguish between data and the next data on one line, the transmission speed is promised in advance or a reference clock is transmitted together so that it can be identified.
  For reference, communication speed is expressed in baud rate or bit rate. Baud rate refers to the number of modulations per second or the number of clocks(＝frequency). In generic digital communication, the baud rate and the bit rate are the same and are often used interchangeably. Here, bit rate is the number of bits per second, and bps(Bit Per Second, lowercase) is used as a unit. And, in the case of a clock, it is good to understand the internal structure if you think of it as a square wave with a constant frequency and duty ratio as used in the memory structure.

 

 

The above relative characteristics are summarized as follows.

 

Comm. Type	Parallel	Serial
Number of lines	Many	Few
Trans. speed	Fast	Slow
Effective distance	Short	Long
Production cost	Increase	Reduction

 

As such, in the case of parallel communication, the available places are limited, so communication generally referred to means serial communication in this blog.

 

3. Communication characteristics – Synchronous and asynchronous

In communication, when a transmitter transmits data, it is called synchronous communication by putting a clock and sending it together like a register. The receiver only needs to interpret the data in response to this clock, it can be recognized quickly and thus the communication speed is also improved. However, there is a problem in that the clock is not data sent from the transmitter and only takes up the line, increasing the production cost. In addition, the clock to be transmitted has to be continuously managed in one side, and it is radiated in the form of an electromagnetic field having the frequency of the clock and affects the surroundings. The higher the frequency of the clock, the worse it is.
  Therefore, the clock line is removed and the transmitter and the receiver communicate by promising the transmission speed in advance. This is called asynchronous communication. The overall communication speed is limited because the receiver must recognize the change several times faster than the promised speed. However, unless a very high speed is required due to a large amount of data, the clock line is eliminated, thereby reducing the cost and enabling communication in an environment in which one of the sources of communication errors is removed.

 

 

4. Communication characteristics – Full-duplex and half-duplex

Assuming that the transmitter and receiver are combined into one structure, transmission and reception are possible at the same time as in a telephone because a transmission line and a reception line are made separately, which is called full-duplex communication. There is no interruption in communication due to transmission during reception, so data flow is smooth and quick response is possible.
  However, if there is no need for a quick response, one line is in a state of being unused alternately, which can also be regarded as an unnecessary line. Thus, half-duplex communication means that the lines of the transmitter and the receiver are merged into one so that reception is impossible during transmission and transmission is not possible during reception, like a walkie-talkie. In this communication, transmission and reception are not performed at the same time, it may be necessary to manage the transmission time point and the expected reception time point separately.

 

 

5. Communication characteristics – Single-ended signal and differential signal

When transmitting information in communication, sometimes the transmitted and received contents do not match. If there is no problem in the line itself, it is possible to suspect information inconsistency due to the electromagnetic field outside the line. The source of this problem is often called noise.
  When transmitting in communication, the existing method of using one line to transmit data in one direction is called a single-ended signal, the solution to the noise of this line is to apply a high voltage to make the response to the noise insensitive. However, as the communication speed increases, the voltage is lowered than before and the signal slope is adjusted more steeply, and the influence of external noise becomes severe.
  Therefore, it is recognized as a method of comparing the potential difference between the two signals by changing to a pair of lines composed of a noninverted signal and an inverted signal. Since only the difference between the two lines is recognized, the same applied noise does not affect the difference between the two lines. By adding a line in this way, the effect of noise can be ignored, and this method is called a differential signal. Although this method significantly improves the effect on noise and contributes to the speed improvement of overall communication, there is also a manufacturing difficulty in that a pair of lines must be of the same length and must always be closely attached or twisted so that the effect of noise is equal. In addition, as the number of lines increases, the cost also generally increases.

 

 

6. Conclusion

In addition to these, communication characteristics include data structure, distance limitation, threshold voltage, and multiple communication, just be aware and get a detailed look at the communication when you see it.