Connect with us

RS232-RS485

Discussion in 'General Electronics Discussion' started by Tron9000, Aug 24, 2011.

  1. Tron9000

    Tron9000

    9
    0
    Aug 24, 2011
    First post, so here goes.

    Apologies if this is not in the right category.

    I've been asked to design a RS485, multidrop network to interface with data terminals (DCE) that spit their information out in RS232. The problem is I haven't touched anything to do with RS485 since uni - 5 years ago!

    The reason behind using RS485 is that we may need to connect more DCE's at a later date.

    I've read up a little about it here:http://www.lammertbies.nl/comm/info/RS-485.html, but am still a little fuzzy on the subject and wikipedia hasn't helped at all (goes mostly into the history if anything!)

    I've been looking at RS232 - RS485 conversion by searching the web and have found very little.

    My question is:
    Am I right in thinking that you can't just plug in an RS232 DCE on a RS485 network? (from what I understand slew rate would be a problem of one)

    And is there a simple solution - IC, circuit with as few components as possible to convert RS232 to RS485?

    I did find this circuit: http://www.rmv.com/232-485.pdf - would this be a valid solution?

    Has anyone done something like this, and if so, what pearls of wisdom can you offer?

    Many thanks!
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,220
    2,695
    Jan 21, 2010
    It's a long time since I was doing any work with serial networks (thinks back to running terminals over lines several km in length).

    I'm almost 100% certain that you need a converter fro RS485 vs RS232. I'm not sure that RS232 would cope very well in a multidrop situation because it's simply not designed for that.

    Sorry I'm not really helpful, but I wanted to make sure you knew you weren't being ignored :)
     
  3. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    Check out the technical library at B&B Electronics.
    http://bb-elec.com/technical_library.asp

    They also have all the 232/485 interface products that you might need. Interfacing a 232 device to a 485 device can be fairly simple; however, interfacing a 232 device to a 485 network can be tricky. RS485 uses tri-state line drivers whereas RS232 does not, so the logic in the RS232 device needs to account for that. Otherwise you will get signal collisions like on a shared Ethernet bus (does anyone still use those?)
     
  4. Tron9000

    Tron9000

    9
    0
    Aug 24, 2011
    Thanks, that's helped a bit more to understand.
     
  5. JoeyAVR

    JoeyAVR

    16
    0
    Aug 25, 2011
  6. Tron9000

    Tron9000

    9
    0
    Aug 24, 2011
    Excellent!

    I knew an IC solution was around
     
  7. Tron9000

    Tron9000

    9
    0
    Aug 24, 2011
    Just hada a look on http://www.findchips.com

    its quite a rare IC.....not to mention a bit expensive.

    Reckon it could be done by a mirco controller?
     
  8. JoeyAVR

    JoeyAVR

    16
    0
    Aug 25, 2011
    A micro can do protocol translations, but won't handle voltage level shifting.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-