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RS232

Page history last edited by wilbo666 6 years, 7 months ago

    1. Introduction
      1. Signal Levels
      2. Idle State
    2. RS232 DTE & DCE
    3. RS232 Serial Port Pinouts
    4. RS232 Serial Cables
      1. DTE - DCE (Standard Cable)
      2. DCE - DCE or DTE - DTE (Null Modem Cable)
    5. RS232 Listener Cable
    6. References

     

    Introduction

    This page provides information in regards to the RS232 standard often used in serial communications.

     

    Signal Levels

    The following applies to all RS232 signals, TxD, Rxd, CTS, RTS, etc.

     

    Logic 1 = -3V to -15V

    Logic 0 = +3V to +15V

    Undefined = -3V to 3V

     

     

    Idle State

    The idle state of a RS232 Transmit pin (TxD) is a logic 1 (-3V to -15V).

     

    RS232 DTE & DCE

    DTE = Data Terminal Equipment, i.e. PC.  DTEs should be fitted with Male connectors.

    DCE = Data Communications Equipment, i.e. MODEM.  DCEs should be fitted with Female connectors.

     

     

    RS232 Serial Port Pinouts

    The most common RS232 serial connectors are DB9 and DB25.

     

    DB9 Pin
    		 DB25 Pin  Acronym Full name Direction (DTE) Meaning
    1
    8
    DCD
    		 Data Carrier Detect
    DTE <-- DCE
    		 Modem connected to another
    2
    3
    RxD
    		 Receive Data
    DTE <-- DCE
    		 Receives bytes into PC (DCE to DTE)
    3
    2
    TxD
    		 Transmit Data
    DTE --> DCE
    		 Transmits bytes out of PC (DTE to DCE)
    4
    20
    DTR
    		 Data Terminal Ready
    DTE --> DCE
    		 I'm ready to communicate (DTE)
    5
    7
    SG
    		 Signal Ground                                   
    6
    6
    DSR
    		 Data Set Ready
    DTE <-- DCE
    		 I'm ready to communicate (DCE)
    7
    4
    RTS
    		 Request To Send
    DTE --> DCE
    		 RTS/CTS flow control (DTE to DCE)
    8
    5
    CTS
    		 Clear To Send
    DTE <-- DCE
    		 RTS/CTS flow control (DCE to DTE)
    9
    22
    RI
    		 Ring Indicator
    DTE <-- DCE
    		 Telephone line ringing

     

    RS232 Serial Cables

    The following have been copied from http://www.bb-elec.com/Learning-Center/Serial-Connectivity.aspx

     

    DTE - DCE (Standard Cable)

     

    DCE - DCE or DTE - DTE (Null Modem Cable)

    RS232 Listener Cable

    A simple listener can be made for half duplex systems (NOTE: This listener cable will NOT work on full duplex systems).

     

    The below circuit relies on pull down resistors inside the listener RS232 port.  If this is not the case then large value resistors (e.g. 4k7Ω) can be fitted in parallel with the diodes.

     

    Simple listener that uses two serial ports, one to receive data transmitted from the PC and one to receive data transmitted from the device.

     

    References

    http://en.wikipedia.org/wiki/RS-232

    http://en.wikipedia.org/wiki/Serial_port

    http://www.aggsoft.com/rs232-pinout-cable/pinout-and-signal.htm

    http://www.bb-elec.com/Learning-Center/Serial-Connectivity.aspx

     

     

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