Pinout rs232 rg45. COM port pinout
Electrical signal levelsRS-232 is a data transfer interface between two devices at a distance of up to 15 meters. The exchange is made by wire digital signals with two voltage levels.
Logic "0" is transmitted with a positive voltage (+5 to +15 V for the transmitter), and a logic "1" is transmitted with a negative voltage (-5 to -15 V for the transmitter).
RS-232 pinout for DB-9 connector
| Contact | Designation | Direction | Name | Description |
| 1 | CD | Entrance | Carrier Detect | Carrier Detect |
| 2 | RXD | Entrance | Receive Data | Data reception |
| 3 | TXD | Exit | Transmit Data | Data transfer |
| 4 | DTR | Exit | Data Terminal Ready | End equipment readiness |
| 5 | GND | --- | System Ground | common wire |
| 6 | DSR | Entrance | Data Set Ready | Readiness of transmission equipment |
| 7 | RTS | Exit | Request to Send | Transfer Request |
| 8 | CTS | Entrance | Clear to Send | Ready to transfer |
| 9 | R.I. | Entrance | Ring Indicator | Call signal presence |
Type of cable used in our products
Our interface converters use a modem (straight through) cable. This means that Tx and Rx are swapped on the converter side. "Handshaking" overhead signals are not used, converted, or transmitted. On the converter side, pins 1,4,6,7,8,9 are not connected.
Distance and data rate
The length of the cable depends on the Maximum Data Rate. The longer the cable, the greater its capacitance, and a slower speed is required for reliable transmission. The maximum distance is considered to be 15 m, but this is not standardized. The table below shows an approximate relationship between cable length and communication speed.
start bit- mandatory bit, indicating the beginning of the transmitted byte.
Data- 7 or 8 data bits. The least significant bit is transmitted first.
Parity bit- optional bit. Can be used for the following purposes:
- parity check (EVEN), complements the transmitted character so that the number of ones in the transmitted character is even;
- odd parity check (ODD), complements the transmitted character so that the number of ones in the transmitted character is odd;
- byte marking (MARK) in 9-bit mode is set to one to allocate a byte of the device address;
- byte marking (SPACE) in 9-bit mode is set to zero to indicate the data byte of the transmitted packet;
If the parity bit is not used, then "NONE" is set in the corresponding COM port settings.
Stop bit- mandatory bit, indicating the completion of the transmission of the byte.
When compared to later interfaces such as , and , has lower transmission speed, short maximum cable length, large voltage swing, large standard connectors, no multipoint capability and limited multidrop capability. In modern personal computers, has displaced RS-232 from most of its peripheral interface roles. Many computers no longer come equipped with RS-232 ports (although some motherboards come equipped with a COM port header that allows the user to install a bracket with a DE-9 port) and must use either an external or an internal expansion card with one or more serial ports to connect to RS-232 peripherals. Nevertheless, thanks to their simplicity and past ubiquity, RS-232 interfaces are still used—particularly in industrial machines, networking equipment, and scientific instruments where a short-range, point-to-point, low-speed wired data connection is adequate.
This PC serial port interface is single ended (interconnect two devices only, via ), the data rate is less than 20 kbps. RS232 is the voltage loop serial interface with full-duplex communication represented by voltage levels with respect to system ground. A common ground between the PC and the associated device is necessary. Hot-plug isn't supported, but sometimes allowed. Nowdays only 9-pin connector is still in use for PCs.
| DE-9 Pin | signal name | Dir | Description |
|---|---|---|---|
| 1 | DCD | Data Carrier Detect | |
| 2 | RXD | Receive Data | |
| 3 | TXD | Transmit Data | |
| 4 | DTR | Data Terminal Ready | |
| 5 | 0V/COM | 0V or System Ground | |
| 6 | DSR | Data Set Ready | |
| 7 | RTS | Request to Send | |
| 8 | CTS | Clear to Send | |
| 9 | R.I. | Ring Indicator |
Note: Direction is DTE (Computer) relative DCE (Modem)
Standard RS232 data packet
RS232 data is usually sent as a packet with 7 or 8 bit words, start, stop, parity bits (may be varied). Sample transmission shown on picture: Start bit (active low, usually between +3v and +15v) followed by data bits, parity bit (depends on protocol used) and finished by stop bit (used to bring logic high, usually between -3v and -15v).
Sample RS232 serial port device. How serial mouse works
A typical PC mouse controlling system has the following parts: sensors -> mouse controller -> communication link -> data interface -> driver -> software. Sensors are the movement detectors which sense the mouse movement and button swiches which sense the button states. Mouse controller reads the state of those sensors and takes acount of current mouse position. When this information changes the mouse controller sends a packet of data to the computer serial data interface controller. The mouse driver in the computer received that data packet and decodes the information from it and does actions based on the information.
PC RS232 serial mouse voltage levels:
Mouse takes standard RS-232C output signals (+-12V) as its input signals. Those outputs are in +12V when the mouse is operated. Mouse takes some current from each of the RS-232C port output lines it is connected (about 10mA). Mouse send data to computer in levels that RS-232C receiver chip in the computer can uderstand as RS-232C input levels. Mouse outputs are normally something like +-5V, 0..5V or sometimes +-12V. Mouse electronics normally use +5V voltage.
Serial device hardware implementation
PC serial mouse uses typically DTR and RTS lines for generating +5V power for microcontroller circuit in the mouse. Because typical optomechanical mouse also needs power for 4 leds in the optocoupler movevement detectors, there is not much power to loose. A typical approach is to use diodes to take current from DTR and RTS lines and then feed it through resistor to all of the (infrared) leds in the movement detectors. The positive power supply is usually taken from RTS and DTR lines (just after the diodes and before the resistor going to leds). The negative supply for transmitter is taken from TD pin. A typical PC serial port mouse takes 10 mA total current and operates at voltage range of 6-15V. The data itself in sent using standard asynchronous RS-232C serial format:
Start D0 D1 D2 D3 D4 D5 D6 D7 Stop Logic 0 ___ ___ ___ ___ ___ ___ ___ ___ ___ +3..+15V | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Logic 1 | | | | | | | | | | -3..-15V___| |___|___|___|___|___|___|___|___|____
Serial mouse pinout explanation
| Pin | Signal | Description |
| shell | Protective Ground | |
| 3 | TD | Serial data from host to mouse (only for power) |
| 2 | RD | Serial data from mouse to host |
| 7 | RTS | Positive voltage to mouse |
| 8 | CTS | |
| 6 | DSR | |
| 5 | Signal Ground | |
| 4 | DTR | Positive voltage to mouse and reset/detection |
RTS = Request to Send CTS = Clear to Send DSR = Data Set Ready DTR = Data Terminal Ready
When DTR line is toggled, mouse should send one data byte containing letter M (ascii 77) to identify itself. To function correctly, both the RTS and DTR lines must be positive. The lines DTR-DSR and RTS-CTS must NOT be shorted. Implement the RTS toggle function by setting the RTS line negative and positive again. The negative pulse width is at least 100ms. After a cold boot, the RTS line is usually set to a negative level. In this case, setting the RTS line to a positive level is also considered an RTS toggle.
RS232 serial data parameters and packet format
1200bps, 7 databits, 1 stop-bit
Data packet is 3 byte packet. It is send to the computer every time mouse state changes (mouse moves or keys are pressed/released).
D7 D6 D5 D4 D3 D2 D1 D0 1. X 1 LB RB Y7 Y6 X7 X6 2. X 0 X5 X4 X3 X2 X1 X0 3. X 0 Y5 Y4 Y3 Y2 Y1 Y0
Note: The bit marked with X is 0 if the mouse received with 7 databits and 2 stop bits format. It is also possible to use 8 databits and 1 stop bit format for receiving. In this case X gets value 1. The safest thing to get everything working is to use 7 databits and 1 stopbit when receiving mouse information (and if you are making mouse then send out 7 databits and 2 stop bits).
The byte marked with 1. is send first, then the others. The bit D6 in the first byte is used for syncronizing the software to mouse packets if it goes out of sync.
LB is the state of the left button (1 means pressed down); RB is the state of the right button (1 means pressed down); X7-X0 movement in X direction since last packet (signed byte); Y7-Y0 movement in Y direction since last packet (signed byte)
The RS232 interface provides a connection between a personal computer and any equipment or device. It used to be used to connect peripheral devices (mouse, printer and modem) to a PC, but now it is mainly used to connect medical and industrial equipment through the RS-485 interface.
RS232 interface in computer: electrical characteristics, pinout, programming, State management and line state reading, initialization
RS232 in the microcontroller: characteristics, the use of RS232 signals when starting and programming the microcontroller, microcircuits for interface level converters, examples of pairing microcontrollers with a computer via RS232; An example of the use of RS232 when programming microcontrollers ADUC8XX; Microcontroller programmers
Do's and Don'ts of RS232 Interface Application:
Remote system for collecting and processing information from sensors of analog, frequency and discrete signals based on an IBM-compatible computer and MSC-51
RS232 interface wiring (COM port) |
The figure below shows the pin assignment of the nine pin connector type DB9.
The RD and TD pins are used for data transfer. The remaining RS-232 pins are used to indicate the status of devices (DTR, DSR), control data transfer (RTS, CTS) and indicate the status of the transmission line (CD, RI). You will see the complete list of pins listed only in an outdated modem. In other cases, for example, when connecting to a computer, a smaller set of RS-232 interface contacts is used.
The RS-232 interface is mainly used in conjunction with a hardware data transfer module called UART, which has a standardized protocol, but it also does not define connectors, etc. That is, RS-232 complements UART. While the UART is a peripheral module in the microcontroller, the digital inputs and outputs of which do not correspond to the electrical parameters of the RS-232 interface, they are brought together by a special circuit - a level converter. One of the well-known converters between RS-232 and TTL CMOS logic is, for example, the MAX232 chip.
In addition, the RS232 interface contains, in addition to signals (RX, TX), also control outputs - DTR, DCD, DSR, RI, RTS and CTS, which are used to control communication between various devices. For example, with their help, the interface scheme can let you know whether it is ready or not to accept a digital code. Since the original purpose of RS-232 was to connect computers to a modem, some signals were used in it to indicate the status of a telephone line.
Zero is used to connect two devices using a COM port. modem cable, in which the wires are "crossed" in accordance with the purpose of the signals. To connect most devices and a PC, a minimum set of RS-232 interface circuits is sufficient: RD, TD and Signal Ground. For example, the figure below shows a cable diagram for connecting a computer with a com port and a VARIKONT controller, on standard DB9 connectors:
The standard limits the maximum cable length to 15 meters at 9600 bps. It is advised not to combine the cable shield with the signal common, but to connect it to the metal shell of the connector.
All signals in the COM port are potential, with nominal levels of +12V and -12V relative to common. The logical unit corresponds to the level -12V, and zero, respectively, + 12V. RS232 is also called a serial interface, because the data stream is transmitted on one wire bit by bit. If there is no transmission, the line is in a logical one state. The data transfer rate is not standardized, but is usually chosen from the digital range 110, 300, 600, 1200, 2400, 4800, 9600, 19200, 36600, with 54200 bits per second. Basically, an asynchronous mode of operation is used, in which the data goes in frames. Each individual frame consists of data, start, parity, and stop bits. The bits of the data byte are transmitted from the least significant. For proper operation, the transceivers on both devices must match the speed, number of data bits, parity type, stop bit length.
When accurately calculating the time to transfer an array of bytes, along with data bits, all service bits should be taken into account.
The figure below shows the "oscillogram" of one frame when following settings: 8 data bits, odd parity, one stop bit: The start bit always follows the level of logical zero, the stop bit always follows the level of one. The state of the parity bit is set by the transmitter option. The bit complements the number of single data bits to odd, even, in some cases may not be used, may always be one or zero.
Since most computers and microcontrollers do not support RS485, in many cases a converter to RS232 may be required. The diagram below allows you to assemble a simple RS232-RS485 interface converter.
The basis of the circuit is the popular MAX232 and MAX485 microassemblies. The DB-9 connector connects the board to the COM port. Connectors J1 and J2 provide access to the I/O lines of the MAX232, and connector CN1 provides access to the I/O lines of the MAX485 chip. Using jumper J4, an external power supply of 9 to 12 V can be connected to the device, which is converted by the regulator to 5 V. If you are powering the circuit through J1, then check that J4 is open. LED D2 lights up when the power is turned off, diode D1 protects against erroneous polarity reversal.
The RS485 cable is connected to the CN2 connector through resistors R3, R1 and R4 to provide the required impedance. Conclusion A CN1 - control of reception / transmission. If you connect it to ground, then RS485 will work only in receive mode, and if you connect it to Vcc, then it will work in transmit mode.
To connect the MAX232 to the MAX485, connect the C pin of J1 to DI CN1 and the B pin of J1 to the RO pin of CN1.
For those who want to assemble an amateur radio design, below is a drawing of a printed circuit board.
There are some amateur radio designs that are best powered directly from the COM port rather than from the main power supply. Most microcircuits are powered by 5 volts, and the interface is capable of delivering current in the region of 8 mA. The circuit uses only four bipolar transistors, at its output we have 5 V and a short circuit current of up to 19 mA.
The current drawn by the circuit itself is about 0.2 mA. The design is very simple, but it has certain tricks. To meet the requirements of the circuit, it is necessary to take into account the gains of the transistors. In our example, only class B devices are used, the gain of which is from 220 to 280. Only the positive part of the voltage from the port passes through the diodes D1-D3. Current limitation is implemented using the resistance R1 and T1. As soon as the voltage across the resistance reaches the level of 0.7 V (at a current of 18 mA R1 = 39 ohms), the transistor opens and thereby locks T2, turning off the output voltage. The 5V output voltage is stabilized at D4.
It should be added that the output voltage here has an approximate value. When the voltage across the zener diode and the voltage through T4 are added together, the result is 5.8V output. However, due to T3, the zener diode operates at low currents, and the actual threshold for opening T4 is about 4.9V. The basis of the regulation cycle is the resistance R2 and T2 . It is required to select R2 with a high resistance (from 1.5 MΩ), because this limits the maximum current flowing through the transistor T2. To get 19 mA output, the base of T2 must receive exactly 1/220 (gain) of 19 mA, and the current going to the base of T3 must be 1/220 of 80 µA. With an input voltage of 9 V, the voltage drop across R2 reaches a level of 3.3 V, and a current of 2.2 μA will flow. Transistor T3 will multiply it by 220, bringing it to 0.5 mA.
Schemes for desoldering connecting cables of equipment used in trade!
Wiring diagram for computer port COM - rs232, DE-9, DB-9, CANNON9
RS-232 (Recommended Standard 232)- in telecommunications, the standard for serial synchronous and asynchronous transmission of binary data between the terminal (English Data Terminal Equipment, DTE) and the end device (with typos com - ssh, kom, rs232 - rc 232, ky232).
Working principle of rs232By structure, this is a conventional asynchronous serial protocol, that is, the transmitting side outputs 0 and 1 to the line in turn, and the receiving side tracks them and remembers them. Data is transmitted in packets of one byte (8 bits). First, a start bit is transmitted, opposite the polarity of the idle line state, after which the frame is transmitted directly useful information, from 5 to 8 bits. Seeing the start bit, the receiver waits for the T1 interval and reads the first bit, then reads the remaining information bits at T2 intervals. The last bit is a stop bit (idle line status) indicating that the transfer is complete. Perhaps 1, 1.5, 2 stop bits. At the end of the byte, before the stop bit, a CRC parity bit (for transmission quality control) can be transmitted. It allows you to detect an error in an odd number of bits (used, since an error of 1 bit is most likely).
ConnectorsDevices for serial communication are connected by cables with 9- or 25-pin D-sub connectors. They are usually referred to as DE-9 (or incorrectly: DB-9), DB-25, CANNON 9, CANNON 25. Initially, RS-232 used DB-25, but since many applications used only a subset of the pins provided by the standard, it became possible to use for these purposes, 9-pin DE-9 (D-subminiature) connectors, which are recommended by the RS-574 standard.
StandardThe Electronic Industries Association (EIA) develops standards for data communications. EIA standards are prefixed with "RS". "RS" means recommended standard, but now the standards are simply referred to as "EIA" standards.
RS-232 was introduced in 1962. The standard evolved, and in 1969 the third edition (RS-232C) was introduced. The fourth edition was in 1987 (RS-232D, also known as EIA-232D). RS-232 is identical to CCITT V.24/V.28, X.20bis/X.21bis and ISO IS2110 standards. The most recent modification is modification "E", adopted in July 1991. as standard EIA/TIA-232E. There are no technical changes in this version that could lead to compatibility issues with previous versions of this standard.
in computer ports accepted designation F (Female) - "mother" - plug socket, M (Male) - "father" - plug with pins.
It should be noted that the rs232 cable length according to the specification is 15 meters. But with the help of high-quality shielded twisted-pair wire, they successfully work at a distance of about 110 meters, for example, Glave and a receipt printer. It should be borne in mind that the higher the exchange rate, the more interference and the shorter the working distance. But at the same time, under an hour, there is equipment that, with a wire length of more than one and a half meters, does not work, or works intermittently.
Moreover, under an hour, replacing equipment does not give any effective result. As a result, here, if possible and of course with software support, for example, in the same case with a kitchen order printer, a print server is installed by connecting a local network (according to the standard, from point to point, the working distance increases to 200 meters, instead of 15 meters for port). Assign IPs to print servers, and plug in the same standard one and a half meter wire from the com port of the print server and the com port of the receipt printer.
Adapted from http://ru.wikipedia.org/wiki/RS-232.
Wiring diagram for computer port COM - rs232, DE-9, DB-9, CANNON9:
RS-232C specification on the example of universal asynchronous transceivers of microcircuits - UART used on IBM PCs:
Wiring diagram for the most common com port cables
Here are those without which you can not live a day. The most common of course is the rs232 null modem cable - the rs232 cable.
It should be noted that some cords are sold in computer stores at quite affordable prices. At the same time, the rs232 db9 connector can be found in some places at a price of 15-20 rubles. for the contact pad and 10 rubles for the case. This is usually the minimum price per connector. Therefore, under an hour it is easier and cheaper to buy a ready-made cable rs232 cord com.
However, as a rule, Chinese products in terms of quality wish for the best both in terms of the cross-section of the wires in the inside .. more precisely, its complete absence and the fragility of the corrugation of the wire.
Pinout COM - RS232 cable - do it yourself:
Russia Copyright site 2009 - 2019
Initially, when they appeared personal computers , with them came at once a few not God knows how tricky, but quite successfully working in combination with the rest of the filling, ports or circuit interfaces. The word port denotes the method of data transfer. It's like a cell of memory. Only in RAM information is recorded and lies there until some program needs it, until the program processes it (or the program itself is still needed on someone's computer).
Port and memory
That is, the program will read the data from the memory to the processor, do something with it, maybe get some new data from this information, which it will write to another place. Or the given itself will simply be rewritten to another place. In any case, in memory, information that was once recorded can either be read or erased. The cell is obtained as a chest, standing against the wall. And all memory consists of a cell, each cell has its own address. Just like chests standing in a row against the wall in the cellar of a miserly knight.
Well, the port can also be imagined as a cell. Only such a cell at the back has a window leading somewhere behind the wall. You can write information into it, and the information will take it and fly out the window, although for some time it will be in the cell in the same way as in a regular cell random access memory.
Or vice versa, information can “arrive” into the port cell from the window. The processor will see this and read this new information that has appeared. And he will put it into action - rewrite it somewhere, recalculate it along with some other data. It can even write it to another cell. Or to another cell-port, then this information received via the first port can "fly away" into the window of the second port - well, this is how the processor will dispose. Rather, the program, which at this moment commands the processor and processes the data recorded in memory and coming from the ports.
Simple and beautiful. These ports were called immediately - I / O ports. Through some of them, data is sent somewhere, through others - from somewhere it is received.
Well, then the circle begins. There is one device, and there is another. And now there is a chain of characters, each of which consists of separate binary bits, and this chain needs to be transmitted. How to transfer? You can immediately transfer a whole character along a line of 8 wires - one wire = one bit, then the code of another, then the third, and so on, until you transfer the entire chain.
And it was possible to unfold each bit not in space (along the wires), but in time: first, transfer one bit of the symbol, then the second, and so on eight times. It is clear that in the second case, some additional means are needed to unfold the symbols in this way in time.
Parallel and serial
And the transfer speed will be different:
It turns out that each option has its pros, but also its cons.
- Eight bits at a time (that is, byte by byte) is faster to transfer, but you need eight times more wires
- To transfer one bit at a time - you need only one information posting, but it will be 8 times slower.
So in the first case they called the transmission parallel, and in the second case - serial.
Port Interface
And the whole system of such transmission - in one case so, in the other - that way, called interface. One interface is parallel, the other is serial. Almost the same thing, ports, one parallel, the other serial.
How is the concept of a port different from the concept of "interface"? AT modern technology words not only appear, they grow and receive "education". And like people, they can become narrow specialists, or they can become "amateurs". Here is a typical amateur word - "interface". Because it is “a plug for every hole”. Interfaces are:
And the meaning of the word is something in between. Inter - between, face - face. It turned out beautifully, so it is used everywhere. For example, user interface Windows systems- this is the screen face of the system, designed to communicate with a person.
And it consists of a picture drawn on the screen + the rules for the operation of each element of the picture (for example, click on the button on the screen with the mouse - it will be pressed) + the rules for the response of each element and the entire system as a whole + all the hardware involved in the dialogue (mouse, keyboard, screen) + all programs that provide dialogue both from the side of the entire system and from individual devices (drivers).
They didn’t mention only a person, but since he is also part of the interaction, he must have the knowledge and skills to work in the system, and for this there are training programs, help systems ... And from all this a beautiful and capacious word arises: interface.
In our theme, interface means things a little more simple.
These are hardware + software transfer + transfer rules. Hardware is understandable. But the software on computers and in modern means connections are always and everywhere. It even happens like this: first, something functional is created on some hardware base, which is not executed immediately, but using specially written programs. And the programs are all customizable.
And gradually, as you work new feature(or functional block), the programs that “make” it - and they differ from hardware in that they can be easily configured - are brought to some kind of state optimal setting. Which is no longer necessary to configure. And then the program new version functional block can be replaced by a hardware-made substitute for the software part. For example, "sew up" an optimally working well-tuned program permanent memory . Or come up with a special logical circuit that will do exactly the same thing that the optimally tuned program did - without shying away and sometimes not forgetting all its useful settings.
Therefore, such an interface is often called - software and hardware.
Transfer rules are needed so that at both ends of the interaction the same things are understood (and processed) in the same way. Are we talking about impulse transmission? This means that the impulses must be exactly the same.
For example, for 1 bit to come in the form of +12 or +15 volts of voltage drop from zero. And so that it was in the form of a rectangle, or a sharp surge - the peak of which was necessarily no less, well, + 5 volts, and it is not very necessary to introduce an upper limit, for example. This is because when impulses are transmitted over some distance, electrical signals tend to weaken and “smear”.
If strictly 12 volts are sent from one end, then 3 volts can reach the other, and this can be regarded by the receiving system simply as noise in the line, and the transmitted information will be lost.
The meaning of impulses must also be understood in the same way. And impulses can be informational, service, synchronizing. And in general, for example, not impulses, but simply constant pressure. Which can be used at the other end to power a small device.
And the very wires themselves, which were discussed at the very beginning, should also be understood equally. Here it must be said right away that it never happens that there is one posting. There are even two wires in the cable for the phone, but normally it is supposed to have four wires in the cable. And data interfaces always have several conductors. Some of them are informational, some are service. And this is what should be equally recognized at both ends of the interaction. And the wires are recognized as? By color, if in the cable and by location, if in the connection contacts.
The word port is simple and also not entirely unambiguous. But the meaning is similar: something that loads something onto something and sends it somewhere. Or vice versa, something that accepts something and unloads something from it. The meaning is almost the same as the hardware-software interface, but somehow more concise. And stricter, as in the Navy (“They will tell you - don’t argue ... but we don’t argue ...”). Only our signals do not travel by sea, but by cable.
COM port pinout
The pinout has no connection. with crucification, although, like wires running freely in one cable sheath, they are disassembled to the sides and hard soldered to their pins, similar to crucification. A pin, in English “pin”, a pin, and therefore a pinout, the word is already a computer-communications “pro-English” jargon. Means - soldering wires on the pins on the connector.
The shape of the connector, the order of the wires (pins) in it, the purpose of each pin, as well as the voltage ratings and the meaning of the signals in each, are part of the interface. Typically, all of this information is collected in a single document called a port specification. Such a simple and clear plate on one page. In other kinds of interfaces, something like this might be called a "protocol". And here it is also simply called "pinout".
Serial COM Ports
Computer COM ports are a connection of a "long-range" computer complex. Unlike parallel ports and cables leading to "heavy" devices - printers, scanners, Com-ports connected "light" units to the computer - a mouse, a modem. The first computer-to-computer interfaces (via "null-modem"). Further, when spread local networks , and mice began to be connected via the same connector as the keyboard - port ps / 2 (pe-es-in half) - com port was somehow forgotten.
The renaissance came with the advent serial interface USB. Here is the circle movement. Now on USB you can find, in addition to flash drives, both USB mice and USB keyboards. Printers, scanners, modems - all peripherals are now on USB, I forgot about thick and solid parallel LTP - cables that had to be screwed on each side with 2 bolts. And there are two signal wires in these USBs (in fact, there is one channel, one direct signal, the other is the same - inverse) and two - power and case.
There were several previous serial COM ports. The smallest and most sought after A 9-pin port (D9) to which most devices were connected: mice, modems, null modem cables. The contacts were arranged in two rows, 5 and 4 in a row, resulting in a trapezoid. Hence the name D9. On the "mother" the numbering went from left to right and from top to bottom:
1 2 3 4 5
COM port pinout, port RS232, 9 pins.
| № | Designation | Type of | Description |
|---|---|---|---|
| 1 | DCD | Entrance | High from the modem when it receives the partner modem's carrier |
| 2 | RxD | Entrance | Incoming data pulses |
| 3 | TxD | Exit | Outgoing data pulses |
| 4 | DTR | Exit | A high level (+12V) indicates that the computer is ready to receive data. The connected mouse used this pin as a power source. |
| 5 | GND | General | Earth |
| 6 | DSR | Entrance | Ready for device transfer |
| 7 | RTS | Exit | Responsiveness of the partner device |
| 8 | CTS | Entrance | Ready to receive data from a partner |
| 9 | R.I. | Entrance | Computer informing signal incoming call received by the modem from the communication line |
