RS-232 interfaces: overview of the standard and types of dimensions

In the world there are a huge number of connectors, slots, interfaces. Identify them and know everything to a simple user is almost impossible. When a newcomer decides to assemble a personal computer on his own, there are many questions regarding compatibility. Today we learn what RS-232 interfaces are.

The concept of

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'll figure it out further in this. This standard refers to the physical layer and was designed as a "partner" for the asynchronous interface. Most often, when recalling RS-232, experts mention a serial port of the PC.

It so happened that he was often used in telecommunications. Now it is known to everyone thanks to the development of computers. It is connected to the PC in case of need for high data transfer rates, and also if the synchronized device is not at a far distance. If we have a computer for office work or entertainment, the RS-232 interfaces are replaced with USB.

History

In the middle of the last century, active development of technologies, in particular, telecommunications, began. Each company that produced certain equipment developed its own standard for data transmission. Accordingly, it was difficult to use such devices, since there were compatibility problems.

To solve this issue forever and standardize everything that has already been achieved, in 1962 a special association was organized. She formed recommendations for the manufacturer, which called the "Recommended Standard 232". That's how it became necessary to develop RS-232 interfaces.

Now the character encoding was in the limits of 5 to 8 bits. The signal voltage did not rise above +25 V and did not drop below -25 V. It was possible to organize service signals, which in general were not necessarily used. Data transmission occurred in two modes: synchronous and asynchronous. Thanks to all the installed features, the standard is ideally suited for telecommunications equipment.

Development

Already seven years after the founding, new editions began to appear. The RS-232C was redesigned in connection with all the shortcomings that could be detected during this time. It was decided to assign 25 contacts to the DB25 connector. This option was really "work on the mistakes", so the time did not change for a long time and became the basic one 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 novelties there were already 4 such transmitters, which received the name COM-port.

The development of such standards has been gaining 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 rights from one company went into the other, a couple of variations of the standard were released. In general, nothing new has been introduced into RS-232 interfaces.

Job

Due to this standard, it became possible to transmit data or special signals between two devices, one of which is a terminal, and the other is a communication one. Transmission is carried out to 15 meters, and the maximum speed can reach 115200 baud. Interestingly, the interface is easy to use and programming. Ego is often used if you need to extend the distance. Experts simply proportionally reduce the speed.

Objectives

It is known that the serial interface RS-232 was first applied from a telephone modem to a PC. Because of this, soon got rudiments, among which was a separate line called "Bell". Over time, Internet devices changed the connectors and began to connect using USB. The same monitored connector did not disappear from the interface panel, so other manufacturers decided to create compatible cables to their devices to connect to the system. So, computer mice with RS-232 became known.

Now this interface is more often found 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 fixed systems still have this connector. As a result, there are both single slots and a loopback on the motherboard. To make this connector not useless, some provide converters.

Operation

As you know, the monitored hero is a duplex interface. It transmits 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 the logical exponents, then positive voltage is correlated to "zero", and negative, to "one". To ensure that this structure worked properly, 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 flow from the hardware side and adjust special functions.

Lines

Interestingly, this port is equipped with type D, with 25 contacts. Each has its own reduction and direction. Have a full name and are responsible for a certain characteristic. So there are transmitted and received data, request and transmission reset, positive and negative voltage, mode alignment, receiver synchronization, call indicator, etc.

Classes

If the terminal device is in front of us, then its connector will be equipped with contacts, if the connected one is holes. It seems like a standard position, but sometimes there are exceptions. The signals of the RS-232 interface are divided into classes.

Consecutive materials such as TXD, operate with an independent serial transmission channel, which is divided into primary and secondary. The lines work by transferring information and receiving it.

The control type RTS has the word "handshake" in the name. It means the way in which signals with a serial link begin to communicate from one transmission to the actual one. There is a synchronization class. In this mode, the equipment transmits signals to each other, which makes it easier to transfer when decoding.

Converters

Before dealing with the converter of RS-232 interfaces, it is worthwhile to know in principle what it is and what it is necessary for. To be clearer, the converter is an adapter. In the event that the device has one connector, but you need another, you can just buy the adapter. Thus, all the necessary slots either become necessary, or simply do not take up unnecessary space.

In our case, it is possible to use the connection of equipment with RS-232/422/485 interfaces for COM ports. As a result, there is a galvanic isolation of the standards, the transfer of information takes place in difficult conditions with electromagnetic interference. The problem in this case is connected only with the fact that there is not enough simple connection, it is necessary to adjust the program level.

In general, different equipment requires its special technologies to transmit data. Therefore, it is necessary to work with the unification of protocols, to translate data into a single view only if a converter is available - it is impossible. The task of such an adapter is that there is an adaptation of the type of information that is transferred between certain parts of the system with special technologies.

So, the processing of packages takes place at the program stage. The program changes the structure of materials that are transmitted, uses a different protocol.

Classification

Interestingly, any converter of the RS-232 interface (etherne and others) can be characterized by several parameters. So, define the standard, by type of equipment and protocols. Also consider the data transfer rate, which is determined by the maximum number of materials in a certain time.

The next parameter is the possible data transmission distance, based on the maximum distance of the nodes from each other, which can transmit information among themselves, but at the same time preserving its integrity. The transmission line is represented by the environment where the data transfer occurs. Among the parameters is the number of "firewood" and receivers, and also an analysis of the "konketing" scheme of the main components is possible.

Examples

In order for the RS-232 interfaces to work correctly together with RS-485/422, it is necessary to acquire not just a converter but a software control. It is worth remembering that the terminals are not all involved, so out of 10 there are only three transmission / reception of data and signal ground. As a result, the conversion process itself is represented by bit-by-bit processing of data from one form to another. At this point, the protocol conversion does not occur, as well as the transformation of the "firewood" of the I / O port.