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How to switch TX, RX,RTS & CTS from an RS232 port to a tranceiver?

Discussion in 'Electronic Basics' started by David Requena, May 26, 2006.

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  1. Jasen Betts

    Jasen Betts Guest

    not by themselves...
    that won't work. (you've got the diodes backwards)
    seems a little high.

    Bye.
    Jasen
     
  2. Pooh Bear

    Pooh Bear Guest

    I thought so too.

    I also can see some potential issues with using this if the levels involved from
    the various transmitters are different. Esp if one uses gnd for '0'.

    Graham
     
  3. Jasen Betts

    Jasen Betts Guest

    0 is typically +3-12v. DYM gnd for 1 ?
     
  4. You may want 'disabling'.
     
  5. John O'Flaherty ha escrito:
    Yes, that's what I meant. Thanks :)
     
  6. This "ancient" means 1978 to 1983...
    Yess, indeed.
    ^^^^^^^^^

    Remember: ""Dumb video Terminal" about 1980 ==> ca. 9600 Baud...

    Holger

    PS: Sorry, I do not have that special issue in my collection. I firmly
    believe in one of the articles of Steve Ciarcia's "Circuit Cellar"
    from BYTE, but I cant't find it.
     
  7. Sure?
    In rs-232 the "mark" (the logical 1) is always a negative voltaje (
    anywhere from +3 to +15 depending on where you lookup the info). The
    "space" (logical 0) is a positive voltaje in the same range.

    As it seems most rs232 equipment can cope with the space being
    indicated by 0 volt. In that case I could understand how this circuit
    works; with the diodes placed as drawn.

    As far as I understand, seting the diodes the other way round wold
    require mark being positive voltage and space 0 volt. That for sure
    would not be rs232 signaling by any means.

    Then... what do I know? I could be completely wrong. I expose my
    reasoning only so any one can correct any missconception :)

    David
     
  8. I have doubts as well...

    The (intended) function of the circuit:

    The _input_ of some RS-232 - Device is held to " minus XX" Volt by
    means of a (suitable) resistor which is connected to some source
    of "minus XX" Volt. Neglecting the input-current of the RS232-device.
    One might use a Handshake-signal of the input-devce...

    One or the other *sending* devices wil be able to pull the line
    to "plus YY" Volt through the diode.

    This works well IF the mentioned resistor is neither too low nor
    too high. This of course depends a little on the input-current
    of the receiver and the voltage.

    The circuit comes from the ages of 1488/1499-Chips..!

    And it works only for the 'normal' TX-Date Line, dosn't it?
    Of course, funny things happen if both senders will send at
    the same time :)
    Holger
     
  9. Jasen Betts

    Jasen Betts Guest

    AIUI most equipment can handle mark being 0v.

    with the diodes as shown the voltage will neve get more positive than -9v
     
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