In the world there are a huge number of connectors, slots, interfaces. It is almost impossible for a simple user to identify them and know everything. When a beginner decides to build a personal computer on his own, many questions arise regarding compatibility. Today we will find out what RS-232 interfaces are.
The concept
If you are faced with the fact that you do not know what kind of connector it is and what it is for, then we will figure it out later. This standard refers to the physical layer and was developed as a "companion" to the asynchronous interface. Most often, recalling the RS-232, experts mention the serial port of a PC.
It so happened that it was often used in the field of telecommunications. Now it is known to everyone thanks to the development of computers. It is connected to a PC if high data transfer speeds are unnecessary, and also if the synchronized device is not at a long distance. If we have a computer for office work or entertainment, then the RS-232 interfaces are replaced with USB.
Story
In the middle of the last century, the active development of technologies, in particular telecommunications, began. Each company that was engaged in the production of certain equipment developed its own standard for data transmission. Accordingly, using such devices was difficult, as there were compatibility issues.
In order to solve this issue forever and standardize everything that has already been worked out, in 1962 they organized a special association. She made recommendations for the manufacturer, which she called “Recommended Standard 232”. This is how the need arose to develop RS-232 interfaces.
Now character encoding was in restrictions from 5 to 8 bits. The signal voltage did not rise above +25 V and did not fall below -25 V. It was possible to organize service signals, which in general were not necessary to use. Data transfer occurred in two modes: synchronous and asynchronous. Due to all the established characteristics, the standard is ideally suited for telecommunication equipment.
Development
Seven years after the foundation, new editions began to appear. RS-232C was redesigned due to all the shortcomings that were discovered during this time. It was decided to assign 25 pins to the DB25 connector. This option really became a “work on mistakes”, therefore it did not change for a long time and became the basis for many years to come.
Already in 1983, personal computers using this standard became known. We started using the UART transceiver. In one of the new products there were already 4 such transmitters, which were called COM-port.
The development of such standards began to gain momentum. Manufacturers realized the principle of action in such situations, so the Association itself began to lose dominance. In 1986, RS changed to EIA. When the rights from one company transferred to another, a couple more variations of the standard were released. In general, nothing new has been introduced into the RS-232 interfaces.
Work
Thanks to this standard, it has become possible to transmit data or special signals between two devices, one of which is a terminal, and the second is a communication one. Transmission is carried out up to 15 meters, and the maximum speed can reach 115200 baud. Interestingly, the interface is easy to use and program. Ego is often used if you need to lengthen the distance. Specialists simply proportionally reduce the speed.
Goals
It is known that the RS-232 serial interface was first applied from a telephone modem to a PC. Because of this, he soon acquired rudiments, among which was a separate line “Call”. Over time, Internet devices changed connectors and began to connect using USB. The reviewed connector itself did not disappear anywhere from the interface panel, so other manufacturers decided to create compatible cables for their devices to connect to the system. So, computer mice with RS-232 became known.
Now this interface is more common in highly specialized devices, industrial equipment and microprocessor systems. As a result, on modern netbooks or laptops, the RS-232 interface cable is almost never found. But some motherboards of stationary systems still have this connector. As a result, there are both single slots and a loopback block on the motherboard. To prevent this connector from being useless, some provide converters.
Functioning
As you know, the monitored hero is a duplex interface. It transfers data as an asynchronous serial interface. A binary signal passes through the wire, which received two voltage levels. This is how information is transmitted.
If we consider logical indicators, then a positive voltage is correlated to “zero”, and a negative voltage to a “unit”. In order for this structure to work as it should, the developers use a large number of "firewood" chips. RS-232 interfaces usually have not only standard input and output lines, but also special auxiliary tracks to control the flow from the hardware side and regulate special functions.
Lines
Interestingly, this port was equipped with type D, with 25 pins. Each has its own reduction and direction. They have a full name and are responsible for a specific characteristic. So there are transmitted and received data, transmission request and reset, positive and negative voltage, mode equalization, receiver synchronization, call indicator, etc.
Classes
If we have a terminal device in front of us, then its connector will be equipped with contacts, but if it is connected, then with holes. It seems like a standard position, but sometimes there are exceptions. The signals of the RS-232 connection interface are divided into classes.
Serial materials such as TXD, work with an independent serial transmission channel, which is divided into primary and secondary. Lines work by transmitting information and receiving it.
The RTS control type has the word acknowledgment in the name. It means a way in which signals with a serial communication line begin communication from one transmission to the actual one. There is a synchronization class. In this mode, the equipment transmit signals to each other, which allows to simplify the transfer during decoding.
Converters
Before you understand the RS-232 interface converter, you should know, in principle, what it is and why it is necessary. To make it clearer, a converter is an adapter. In the event that the device has one connector, but you need another, you can just buy an adapter. Thus, all the necessary slots either become necessary, or simply do not take up too much space.
In our case, it is possible to use equipment connection with RS-232/422/485 interfaces for COM ports. As a result, there is a galvanic isolation of standards, the transmission of information takes place in difficult conditions with electromagnetic interference. The problem in this case is only due to the fact that a simple connection is not enough, you will have to configure the software level.
In general, different equipment requires special technologies for data transfer. Therefore, it is necessary to work with the unification of protocols, it is impossible to translate data into a single form only if there is a converter. The task of such an adapter is that there is an adaptation of the type of information that is transmitted between certain parts of the system with special technologies.
So, package processing takes place at the software stage. The program changes the structure of materials that are transmitted, uses a different protocol.
Classification
Interestingly, any RS-232 interface converter (etherne and others) can be characterized by several parameters. So, they determine the standard according to the type of equipment and protocols. Also consider the data transfer rate, which is determined by the maximum number of materials for a certain time.
The next parameter is the possible distance of data transmission, based on the maximum distance of nodes from each other, which can transmit information among themselves, but at the same time maintaining its integrity. The transmission line is represented by the environment, where the data transfer takes place. Among the parameters there is the number of "firewood" and receivers, as well as the analysis of the "connecting" circuit of the main components.
Examples
In order for RS-232 interfaces to work correctly in tandem with RS-485/422, you need to get not just a converter, but software control. It is worth remembering that the terminals are not all involved, so out of 10 there is only a triple of data transmission / reception and signal grounding. As a result, the conversion process itself is represented by bitwise processing of data from one form to another. At this point, protocol conversion does not occur, nor does the transformation of the “firewood” of the I / O port.