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I/O Devices RS232 RS485 RS422 USB Serial Parallel Port PC Interface Protocol

Computer hardware interface Knowledge base site - you will found all about way to Computer hardware interface PC Interface such as rs232, rs485, rs422, usb, serial port, parallel port, port programming, Comport TEST Serial Com Port Test Software.Sample code and more software relevent with interfacing computer.and more document. How to pc interfacing?.- How to hardware interfacing?.

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Intro to Serial Com port
RS232 DB9 Connector Pin Layout

RS232 DB25 Connector Pin Layout
DB25 Serial Convert to DB9 Connector
pins and wires
RS232 RS422 RS485 Compare
Recommended RS232 Software

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- Intro to Serial port

The UART serial port (or just "serial Com 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 using. 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 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 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.


- DB9 DB25 Pins and Wires

Old PC's used 25 pin connectors but only about 9 pins were actually used so today most connectors are only 9pin. Each of the 9 pins usually connects to a wire. Besides the two wires used for transmitting and receiving data, another pin (wire) is signal ground. The voltage on any wire is measured with respect to this ground.

Thus the minimum number of wires to use for 2-way transmission of data is 3. Except that it has been known to work with no signal ground wire but with degraded performance and sometimes with errors. There are still more wires which are for control purposes (signalling) only and not for sending bytes. All of these signals could have been shared on a single wire, but instead, there is a separate dedicated wire for every type of signal. Some (or all) of these control wires are called "modem control lines". Modem control wires are either in the asserted state (on) of +12 volts or in the negated state (off) of -12 volts. One of these wires is to signal the computer to stop sending bytes out the serial port cable. Conversely, another wire signals the device attached to the serial port to stop sending bytes to the computer. If the attached device is a modem, other wires may tell the modem to hang up the telephone line or tell the computer that a connection has been made or that the telephone line is ringing (someone is attempting to call in).

- DB9 DB25 RS232 Wiring

rs232 db9 port pin pc interfacing

The Serial Port have two types.

First serial port use 25 pins or call "DB25" but DB25 has too large.Next, DB9 ( 9 pins Compact and small) have been replace with DB25


parallel port db25 pin hardware interfacing

Convert DB9 to DB25 Pins

Convert db9 to db25 The original pinout 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

Recommended RS232 Software

Look RS232

Look RS232 is a tool for debugging computer connection with peripheral devices hardware interfacing using COM port, such as modem, mini-ATS, projector etc. Its easy to use interface guarantees an easy work with Com-port.

Look RS232 can send data through COM port, receive data from an outer device through COM port, it has port indication as well.

Look RS232 supports connection at the standard speed of 110115200 kbit/s, it supports commands of COM port program control.

Look RS232 supports data input in ASCII, BIN, HEX, OCT formats, keeps log of the sent and received data and commands in ASCII, BIN, HEX, OCT formats, it has an option of time link (relating to COM port activation).

Look RS232 works with system initiated COM ports regardless of whether they are installed on motherboard or on supplementary in/output boards, e.g. VS-Com (Roadrunner) PCI-800H 8-port PCI. Visit site | Download here

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Computer Hardware Interface I/O Devices RS232 RS485 RS422 USB Serial Parallel Interface protocol Com Port Test Comport Checking hardware interfacing