Serial interface RS-232. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Serial interface RS-232. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Computers

Comments on the article

A widely used synchronous and asynchronous serial interface defined by the EIA RS-232-C standard and V.24 CCITT recommendations. It was originally created to connect a computer with a terminal. Currently used in a wide variety of applications.

Serial interface RS-232

The RS-232-C interface connects two devices. The transmission line of the first device is connected to the reception line of the second one and vice versa (full duplex). Software confirmation is used to control the connected devices (introduction of appropriate control characters into the transmitted data stream). It is possible to organize hardware confirmation by organizing additional RS-232 lines to provide status and control functions.

Serial interface RS-232

Standard

EIA RS-232-C, CCITT V.24
Transmission speed 115 kbps (maximum)
Transmission distance 15 m (maximum)
Signal nature voltage unbalanced
Number of drivers 1
Number of receivers 1
Connection diagram full duplex, point to point

The order of exchange via the RS-232C interface
Name Direction Description Contact
(25 pin connector) Contact
(9 pin connector)
DCD IN CarrierDetect 8 1
RXD IN ReceiveData(Received data) 3 2
TXD OUT TransmitData(Transmitted data) 2 3
DTR OUT DataTerminalReady(Terminal Ready) 20 4
GND - SystemGround(System Chassis) 7 5
DSR IN DataSetReady(Data Ready) 6 6
RTS OUT RequesttoSend(Request to send) 4 7
CTS IN CleartoSend(Ready to receive) 5 8
RI IN RingIndicator(Indicator) 22 9

The RS-232C interface is intended for connecting standard external devices (printer, scanner, modem, mouse, etc.) to a computer, as well as for connecting computers to each other. The main advantages of using RS-232C over Centronics are the ability to transmit over much longer distances and the much simpler interconnect cable. At the same time, working with him is somewhat more difficult. Data in RS-232C is transmitted in serial code byte by byte. Each byte is framed by start stop bits. Data can be transmitted both in one direction and in the other direction (duplex mode).

The computer has a 25-pin (DB25P) or 9-pin (DB9P) RS-232C connector. The purpose of the connector pins is given in the table.

The purpose of the signals is as follows:

FG - protective grounding (screen).

TxD - data transmitted by the computer in serial code (negative logic).

RxD - data received by the computer in serial code (negative logic).

RTS - transmission request signal. Active during transmission.

CTS - reset (clear) signal for transmission. Active during transmission. Talks about the readiness of the receiver.

DSR - data readiness. Used to set the modem mode.

SG - signal ground, neutral wire.

DCD - data carrier detection (received signal detection).

DTR - readiness of output data.

RI - call indicator. Indicates that the modem is receiving a call signal over the telephone network.

The most commonly used are three- or four-wire communication (for bidirectional transmission). The connection diagram for a four-wire communication line is shown in Figure 1.1.

For a two-wire communication line, in the case of only transmission from a computer to an external device, SG and TxD signals are used. All 10 interface signals are activated only when the computer is connected to the modem.

The format of the transmitted data is shown in Figure 1.2. The actual data (5, 6, 7, or 8 bits) is followed by a start bit, a parity bit, and one or two stop bits. Having received the start bit, the receiver selects data bits from the line at certain time intervals. It is very important that the clock frequencies of the receiver and transmitter are the same, the allowable discrepancy is no more than 10%. 232, 110, 150 bps.

Serial interface RS-232
Rice. 1.1 Schematic of 4-wire communication line for RS-232C

All RS-232C signals are transmitted at specially selected levels, providing high noise immunity of communication (Fig. 1.3.). Note that the data is transmitted in the inverse code (logic one corresponds to a low level, logic zero - a high level).

To connect an arbitrary RS to a computer via RS-232C, a three- or four-wire communication line is usually used (see Fig. 1.1), but other interface signals can also be used.

Serial interface RS-232
Rice. 1.2 RS-232C data format

The exchange via RS-232C is carried out using calls on specially dedicated ports COM1 (addresses 3F8h ... 3FFh, interrupt IRQ4), COM2 (addresses 2F8h ... 2FFh, interrupt IRQ3), COM3 (addresses 3F8h ... 3EFh, interrupt IRQ10), COM4 (addresses 2E8h...2EFh, interrupt IRQ11). Call formats for these addresses can be found in numerous descriptions of UART (Universal Asynchronous Receiver / Transmitter) serial controller chips, for example, i8250, KR580BB51.

Serial interface RS-232
Rice. 1.3 RS-232C signal levels at the transmitting and receiving ends of the communication line.

Publication: cxem.net

See other articles Section Computers.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Artificial leather for touch emulation 15.04.2024

In a modern technology world where distance is becoming increasingly commonplace, maintaining connection and a sense of closeness is important. Recent developments in artificial skin by German scientists from Saarland University represent a new era in virtual interactions. German researchers from Saarland University have developed ultra-thin films that can transmit the sensation of touch over a distance. This cutting-edge technology provides new opportunities for virtual communication, especially for those who find themselves far from their loved ones. The ultra-thin films developed by the researchers, just 50 micrometers thick, can be integrated into textiles and worn like a second skin. These films act as sensors that recognize tactile signals from mom or dad, and as actuators that transmit these movements to the baby. Parents' touch to the fabric activates sensors that react to pressure and deform the ultra-thin film. This ... >>

Petgugu Global cat litter 15.04.2024

Taking care of pets can often be a challenge, especially when it comes to keeping your home clean. A new interesting solution from the Petgugu Global startup has been presented, which will make life easier for cat owners and help them keep their home perfectly clean and tidy. Startup Petgugu Global has unveiled a unique cat toilet that can automatically flush feces, keeping your home clean and fresh. This innovative device is equipped with various smart sensors that monitor your pet's toilet activity and activate to automatically clean after use. The device connects to the sewer system and ensures efficient waste removal without the need for intervention from the owner. Additionally, the toilet has a large flushable storage capacity, making it ideal for multi-cat households. The Petgugu cat litter bowl is designed for use with water-soluble litters and offers a range of additional ... >>

The attractiveness of caring men 14.04.2024

The stereotype that women prefer "bad boys" has long been widespread. However, recent research conducted by British scientists from Monash University offers a new perspective on this issue. They looked at how women responded to men's emotional responsibility and willingness to help others. The study's findings could change our understanding of what makes men attractive to women. A study conducted by scientists from Monash University leads to new findings about men's attractiveness to women. In the experiment, women were shown photographs of men with brief stories about their behavior in various situations, including their reaction to an encounter with a homeless person. Some of the men ignored the homeless man, while others helped him, such as buying him food. A study found that men who showed empathy and kindness were more attractive to women compared to men who showed empathy and kindness. ... >>

Random news from the Archive

Oblivion molecule 17.11.2017

If you can't seem to forget something, it's possible that your brain simply lacks the neurotransmitter gamma-aminobutyric acid (GABA).

Researchers from Cambridge, the University of Utah and the University of Granada set up the following neuropsychological experiment: young people were asked to play a simple game - watch the color of the figures appear on the screen and press the right or left button on a special remote control, depending on the color of the figure. At first, the participants in the experiment pressed and pressed the buttons until it became a completely automatic action for them.

Then the rules changed: if a person suddenly heard a sound at the same time as the picture, he should not have pressed anything. Now it became more difficult to complete the task, and some, having heard the beep, did not have time to slow down their fingers and still pressed the button - as they had done so many times.

Some, on the contrary, managed to quickly learn the new rules, so that they reacted to the sound correctly. Obviously, here it was necessary to forget that when a figure appeared on the screen, it was necessary to press a button, and, as it turned out, those who had a lot of gamma-aminobutyric acid in their hippocampus did it the fastest. The participants in the experiment, of course, made every effort to forget about the unnecessary action, but, again, only those who had a lot of GABA in the hippocampus were good at forgetting.

Hippocampal activity was monitored using functional magnetic resonance imaging (fMRI). But it is impossible to find out about this or that substance through fMRI - tomography just shows how different brain zones work. However, the authors of the work, together with fMRI, used a variation of the nuclear magnetic resonance method, which helped to estimate the amount of GABA directly in the living human brain.

The hippocampus is considered one of the main centers of memory, and in it, like in all other brain centers, there are inhibitory neurons, the task of which is to turn off the activity of various nerve chains. Inhibitory neurons use GABA to transmit signals, so it’s understandable why some people couldn’t forget to always press the button: inhibitory neurons, due to the lack of their neurotransmitter, could not silence those neural circuits that remembered the initial conditions tasks.

For a healthy psyche, it is important not only to be able to remember, but also to be able to forget. The restructuring of memory is necessary for learning - we already wrote once that in order to remember something, you need to forget something. Moreover, it is believed that many mental disorders, up to schizophrenia, are associated, among other things, with the fact that the brain remembers too much.

From unnecessary information, obsessive thoughts appear, which can cause constant anxiety, depression, hallucinations, etc.; in fact, studies of the brains of patients with schizophrenia have shown that during their lifetime they had problems with the inhibitory neurons in the hippocampus. And the idea of a drug that would act on such neurons, helping us to forget, in the light of new results, looks not only relevant, but also quite real.

Other interesting news:

▪ Electric car Hyundai IONIQ 6

▪ XBee modules certified by the ZigBee Alliance

▪ Belkin Washable Mouse

▪ Huawei Smart Life Air Purifier 1Pro

▪ White graphene for microcircuit cooling

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Note to the student. Article selection

▪ article by Carl Baer. Biography of a scientist

▪ article Where and when did you start renting cars? Detailed answer

▪ article Siberian apple tree. Legends, cultivation, methods of application

▪ article Tuning antennas and circuits using a jammer. Encyclopedia of radio electronics and electrical engineering

▪ article Method for measuring the filament voltage of a kinescope. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages of this page

Home page | Library | Articles | Website map | Site Reviews