RS232 Problem

Discussion in 'General Electronics Chat' started by mohammad2050, Feb 9, 2015.

  1. mohammad2050

    Thread Starter Member

    Nov 14, 2014
    56
    1
    hi
    i have a device with RS232 communication port ,power supply is 9 volt in this device , but As you know Valid signals are either in the range of +3 to +15 volts or the range −3 to −15 volts with respect to the ground/common pin in RS232. do this power supply will not create any problem ?
    when connect directly device to pc RS232 , Do not communicate with each other ! And sometimes drop power supply!
    Do I must use the interface circuit ؟
     
    Last edited: Feb 9, 2015
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you use a MAX232 it has internal charge pump for the ±v .
    Alternatively there are dedicated RS232 drivers & recievers that also require a separate ±v charge pump supply.
    Max.
     
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  3. mohammad2050

    Thread Starter Member

    Nov 14, 2014
    56
    1
    thanks MAX, in your opinion , i must use two MAX232?! (RS232 to ttl and ttl to RS232)
    what is your order of internal charged pump in max232 ?
    [​IMG]
     
    Last edited: Feb 9, 2015
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You would use one on the RX end and one on the TX end, what is meant by your order?
    I have used them for some years now with excellent results.
    Max.
     
    Last edited: Feb 9, 2015
  5. mohammad2050

    Thread Starter Member

    Nov 14, 2014
    56
    1
    Excuse me
    I mean, why should I use MAX232? Why can not directly connect them to each other?(Both is RS232)
    what is internal charged pump in max232 ? why must use separate ±v charge pump supply(Except max232)?
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    They can both be connected together TTL - RS232 then back RS232 - TTL on each end.
    The older technology IC used a few decades ago required the separate charge pump.
    Or do you mean keep at the TTL level?
    Max.
     
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  7. mohammad2050

    Thread Starter Member

    Nov 14, 2014
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    I do not understand that why direct connection do not work!
    why must first convert RS232 to ttl level and then ttl to RS232 level? why directly dont work?
     
  8. ScottWang

    Moderator

    Aug 23, 2012
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    767
    I think you should provide some more infos and photos about your device to clarify what you described.
     
  9. mohammad2050

    Thread Starter Member

    Nov 14, 2014
    56
    1
    [​IMG]
     
  10. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    Buy some 2-terminal bi-colour LEDs and an equal number of 680R resistors - then you can wire up an RS232 connector as an indicator, then you can verify which line are inputs and which wires are outputs, that way you can make sure that you only connect outputs to inputs - then all you have to do is look up the right outputs to connect to which inputs.

    Another possible source of confusion is the distinction between DCE and DTE, where DCE might be a modem and DTE might be the computer - the charts and tables weren't always consistent in how the pins were labled.

    Search for "null-modem cable" you should find connection diagrams that with a bit of careful study, make the ins and outs fairly clear.
     
  11. mohammad2050

    Thread Starter Member

    Nov 14, 2014
    56
    1
    if your mean is RX,TX and GND , Be sure to I've make the correct connections .
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    Too many reasons to caused them can't communicate each other, wrong baud rate, wrong port, wrong setting, etc...
    What's your device?
    I'm not sure why keeping it as secret, so we only can guessing the puzzle?

    Too less infos ... :(
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The program you are using in you PC may also be requesting hardware Handshake, if only using 3wire mode, you need to set XON/XOFF or no H.S., I usually jumper out the H.W. handshake on the P.C. side as a precaution.
    This is 1-4-6 & 7-8 on a 9 pin D.
    Max.
     
    Last edited: Feb 9, 2015
  14. mohammad2050

    Thread Starter Member

    Nov 14, 2014
    56
    1
    my device is ABB aquamaster . Does not matter device name Because RS232 IS RS232 :)
    and I've done all the settings correct!


    i use hiper terminal with flow control set on NONE,
    device side is 3 wire

    I did not test this.
    I test a RS232 Isolator(Buy this) But It does not work !
     
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