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Serail Port (Com port,RS-232) Information

Understand in Serial port,Com Port,RS-232

I thing,you know the comm port ,may be you have not still understand it in control and access it for interfacing to another hardware. We can interface hardware and device with serial port in PC programming(VB,VC++,.NET,Delphi,Pascal,Linux etc.). So,This article help you know about information of using in serail port.
These are like the picture below.




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Most PC's have one or two serial ports. Each has a 9pin connector (sometimes 25pin) on the back of the computer. Computer programs can send data (bytes) to the transmit pin (output) and receive bytes from the receive pin (input). The other pins are for control purposes and ground.
The Serial port or Comm port is I/O(Input and Output) device. An I/O device is just a way to get data into and out of a computer using. There are many types of I/O devices such as serial ports, parallel ports, disk drive controllers, ethernet boards, universal serial buses, etc.

The majority in the Serial Port using was use in communication with RS-232,RS-485,RS422 system. For the Serial port is much more than just a connector. It converts the data from parallel to serial and changes the electrical representation of the data. Inside the computer, data bits flow in parallel (using many wires at the same time). The Serial flow is a stream of bits over a single wire . For the Serial port to create such a flow, it should be convert data from parallel to serial (this process in Computer) on the transmit pin . Most of the electronics of the serial port is found in a computer chip that you had known as a UART.

Wring Pins and Wires Diagram for DB9,DB25 in Serial Port connector

DB9 Male Connector
DB9 Fale Male Connector

Teble below is show inforamtion of Pins and Wries including such as DB25 pins compare with DB9 pins,Comm port I/O address,MODEM wring ,Loop back wring etc.


In the normal pin out for RS232 was developed for a 25 pins sub D connector. Since the introduction of the smaller serial port on the IBM-AT, 9 pins RS232 connectors are commonly used. In mixed applications, a 9 to 25 pins converter can be used to connect connectors of different sizes. As most of the computers are equipped with the DB9 serial port version, all wiring examples on this website will use that connector as a default. If you want to use the example with a DB25, simply replace the pin numbers of the connector according to the conversion The methods of serial data transmission imply that data are transmitted the following way: data are transmitted from transmitter to receiver bitwise simultaneously uing only one line.For this purpose the serial port takes 8, 16 or 32 parallel bits from the data bus and transforms them to get 8, 16 or 32-bit serial bit flow. That's why serial communication got its name - every information bit is transmitted serially one by one.

Understand in Serial Port Communication

For developper must be know in Serial or RS-232 communication in theory when organizing serial communication to transmit the signal from one device to another one should use only two wires are TX / RX signal and ground. But in practical work shows that this way of data transmission is not always usable, especially when data transmission is lengthy.It is connected with the fact that when receiving, the receiver may miss some bits and so they may be lost. This would cause changes in the result of the whole transmission. Even if one bit is lost, this may cause the following: when the whole data batch is received the bits coming after the lost bit may be shifted and erraneous data may be obtained when transforming into parallel code. Regrading The UART serial port (or just "serial port for short" is an I/O (Input/Output) device. An I/O device is just a way to get data into and out of a computer. There are many types of I/O devices such as serial ports, parallel ports, disk drive controllers, ethernet boards, universal serial buses, etc. Most PC's have one or two serial ports. Each has a 9-pin connector (sometimes 25-pin) on the back of the computer. Computer programs can send data (bytes) to the transmit pin (output) and receive bytes from the receive pin (input). The other pins are for control purposes and ground. The serial port is much more than just a connector. It converts the data from parallel to serial and changes the electrical representation of the data. Inside the computer, data bits flow in parallel (using many wires at the same time). Serial flow is a stream of bits over a single wire (such as on the transmit or receive pin of the serial connector). For the serial port to create such a flow, it must convert data from parallel (inside the computer) to serial on the transmit pin (and conversely). Most of the electronics of the serial port is found in a computer chip (or a part of a chip) known as a UART. For more details on UARTs see the section What Are UARTS? But you may want to finish this section first so that you will hopefully understand how the UART fits into the overall scheme of things. That's why in order to achieve reliable serial communication one should overcome all possible errors when receiving data. One of the possible solutions may be application of RS-232-C standard which describes the methods of synchronous and asynchronous data transmission in serial data format.

How to RS-232-C interfacing

The RS-232-C interface is a serial interface of synchronous and asynchronous data transmission defined by the EIA RS-232-C standard and V.24 CCITT recommendations, this interface was initially created to connect the computer with a terminal. The purpose of creating the RS-232-C interface was to maintain connection between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE) using consistent binary data communication. Usually DTE is a terminal or a computer, and DCE - a modem or any other communications device. The transmitting line of the first device connects with the receiving line of the second device and vice versa (by this organizing full duplex). To control the connected devices the programme approval is used (that is introducing control characters into the transmitted data flow). It is possible to organize hardware approval by providing additional RS-232-C lines to maintain status defining and control functions. Website Referrent http://www.tldp.org http://www.lookrs232.org

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