I/O Devices RS232 RS485 RS422 USB Serial Parallel Port PC Interface Protocol
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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 |
Sponsor Link |
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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. |
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- 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 |
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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
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Convert DB9 to DB25 Pins
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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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