Contents. Overview Communication as defined in the RS232 standard is an asynchronous serial communication method. The word serial means, that the information is sent one bit at a time.
Asynchronous tells us that the information is not sent in predefined time slots. Data transfer can start at any given time and it is the task of the receiver to detect when a message starts and ends. Voltages The signal level of the RS232 signal can have two states. A high bit, or mark state is identified by a negative voltage and a low bit or space state uses a positive value. This might be a bit confusing, because in normal circumstances, high logical values are defined by high voltages also.
The voltage limitations are shown below. RS232 voltage values Level Transmitter capable (V) Receiver capable (V) Space state (0) +5 Vdc up to +15 Vdc +3 Vdc up to +25 Vdc Mark state (1) -5 Vdc up to -15 Vdc -3 Vdc up to -25 Vdc Undefined - -3Vdc up to +3Vdc Pinouts View - looking into Male connector View - looking into Female connector Pin No.
Name Dir Notes/Description 1 DCD IN Data Carrier Detect. Raised by DCE when modem synchronized. 2 RD IN Receive Data (a.k.a RxD, Rx). Arriving data from DCE. 3 TD OUT Transmit Data (a.k.a TxD, Tx). Sending data from DTE.
4 DTR OUT Data Terminal Ready. Raised by DTE when powered on. In auto-answer mode raised only when RI arrives from DCE. 5 SGND - Ground 6 DSR IN Data Set Ready. Raised by DCE to indicate ready.
What Is Serial Communication
7 RTS OUT Request To Send. Raised by DTE when it wishes to send. Expects CTS from DCE. 8 CTS IN Clear To Send. Raised by DCE in response to RTS from DTE. 9 RI IN Ring Indicator.
Rs232 Serial Cable
Set when incoming ring detected - used for auto-answer application. DTE raised DTR to answer. Achievable Distances The maximum distance that RS-232 can go varies depending on Baud Rate and also the capacitance of the wire itself. Texas Instruments states that RS-232 maximum cable length is 50 feet, or the cable length equal to a capacitance of 2500 pF. Depending on the cable such as Category 5 Twisted pair the maximum achievable distance at 19200 is 157 feet. Here is a chart showing theoretical limits as various data rates for RS-232 cable length according to Texas Instruments.
Baud rate Maximum cable length (ft) 192 500 4800 1000 2400 3000 Advantages RS-232 is without doubt the best known interface, because this serial interface is implemented on almost all computers available today. Disadvantages One of the main problems with RS-232 is the lack of immunity for noise on the signal lines. However RS-232 suffers from three main problems:. 1) it requires multiple ground points and can create potential ground loops. 2) it picks up noise easily and. 3) it allows only short communication distances.
In order to overcome some of these issues or is the preferred choice. Interfacing to Microcontrollers In order for RS232 to communicate with a Microcontroller such as a Pic16f88 or Atmel, level conversion must first be done because of the voltage levels on TTL is 5 Vdc max and normal RS232 far exceeds voltage limitations and damage will occur. Devices such as a will make the necessary voltage conversion possible for communication to and from TTL devices. External Links.
C# Rs232 Communications
Serial vs Parallel Port Let's consider the advantages and disadvantages of using serial port when compared with parallel port. Serial port has all the advantages of serial data transmission:. The serial port cable can be longer than a parralel port cable, as serial port transmits '1' as voltage from -5 to -12V and '0' as voltage from +5 to +12 V, while parralel port transmits '1' as voltage of 5 volts and '0' as voltage of 0 volts.
At the same time the receiver of the serial port receives '1' as voltage from -3 to -25 V and '0' as voltage from +3 to +25 V. Thus serial port can have maximal swing up to 50 volts, while parralel port has maximal swing of 5 volts. Thus the losses in the cable when transmitting data using serial port are less substantial then losses when transmitting data using parralel port. The number of wires needed when transmitting data serially is less than when the transmission is parallel. Is the external device has to be installed at a great distance from the computer, the cable with three wires is much cheaper than the cable with 19 or 25 wires if the transmission is parallel. Still one should remember that there are interface creation expences for every receiver/transmitter. Further development of serial port is usage of infrared devices which immediately proved popular.
Many electronic diaries and palmtop computers have inbuilt infrared devices for connection with external devices. Another proof of serial port universality is microcontrollers. Many of them have inbuilt SCI (Serial Communications Interfaces), used for communication with other devices. In this case serial interface reduces the number of outputs on the chip. Oxford advanced learner dictionary 10th edition.
Usually only 2 outputs are used: Transmit Data (TXD) and Receive Data (RXD). Just compare that to minimum of 8 outputs when using 8-bit parralel connection. Surely enough serial port has its drawbacks.
The main one is that when organizing serial connection it is always necessary to convert the data into serial code and vice versa. FCoder © 1998 - 2002.