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RS232 detects pulse .... fail

Discussion in 'Electronic Design' started by boki, Oct 7, 2004.

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  1. boki

    boki Guest

    Dear All,
    I have a portable device that has a 5-V to 0-V pulse output(
    without constant frequency, but below 10Hz range), I want this signal
    could be detected by PC RS232 port.

    I try many connection type, the RS232 still can't detect the device

    Do we have to design RS-232 handshake circuits with device output to
    make the RS232 detect that pulse?

    * I don't have to transmit data,just only pulse detection.

    Is that baud rate problem? or ? @@

    Thank you very much for your help.

    Best regards
  2. Boki

    Boki Guest

    short pin.8 pin.4 work...
  3. Rich.Andrews

    Rich.Andrews Guest

    yup. that will do it every time.

  4. Rolavine

    Rolavine Guest

    From: (boki)
    Your not going to get the uart to give you an serial input for that signal, but
    if you check the internal registers you can prob. detect it as a framing or
    overun erorr. I think you can also read the direct state of the receive pin
    via registers, I haven't done that for about 4 years so I don't remember. I
    know you can read the input of some of the other RS232 lines via these
  5. Boki

    Boki Guest

  6. Boki

    Boki Guest

    Why @@?

    pin.8 CTS
    pin.4 DTR

  7. Rich.Andrews

    Rich.Andrews Guest

    I think he meant pins 4 and 8 on the chip. I took it to mean he found the
    CD line.

  8. Boki

    Boki Guest


  9. Rich.Andrews

    Rich.Andrews Guest

    25 pins?


    25 pin
  10. Boki

    Boki Guest

    9 pins :)

  11. mike

    mike Guest

    You have lots of issues.
    The operating system may or may not let you access the port.
    The pulse width may be too narrow to reliably poll the port.
    Polling uses up all the system bandwidth.
    YOu may have to loop back the control lines to get the port to
    work if you use an existing driver.
    You might be able to use the error reporting of the rs232 port.
    Might want to latch the pulse externally and let the rs232 reset it
    after it's recognized.
    A lot depends on what you're trying to do, whether you need accurate
    time information, can you deal with missed pulses...etc.

    I've come to the conclusion that with the increasing unavailability
    of PC ports and port access, you're almost always better off doing the
    real-time stuff in a PIC or other external processor and reporting
    the results over your interface of choice.
  12. The standard RS-232 connector is a 25 conductor DB-25, although
    many PCs (and some other equipment) now use a 9 pin DE-9
    incorrectly called DB-9)

    Serial Port Connections
    Computer (DTE) Modem
    DB-25 DE-9 Signal Direction DB-25
    2 3 Tx Data -> 2
    3 2 Rx Data <- 3
    4 7 Request to send -> 4
    5 8 Clear to send <- 5
    6 6 Data Set Ready <- 6
    7 5 signal ground 7
    8 1 Data CarrierDetect <- 8
    20 4 Data Terminal Ready -> 20
    22 9 Ring Indicator <- 22

    Standard remedy for RS-232 communications problems: if it doesn't
    work, exchange connections on pins 2 and 3.

    Peter Bennett, VE7CEI
    peterbb4 (at)
    new newsgroup users info :
    GPS and NMEA info:
    Vancouver Power Squadron:
  13. The RS-232 data input is designed to receive "characters" sent in a
    specific format - it is not intended to detect random pulses.
    You can use a handshake input line to detect your pulse - but you will
    have to read the UART status register to see it.

    Peter Bennett, VE7CEI
    peterbb4 (at)
    new newsgroup users info :
    GPS and NMEA info:
    Vancouver Power Squadron:
  14. boki

    boki Guest

    Thank you very much for information.

    Best regards,
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