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RS-485 and RS-422

Discussion in 'Electronic Equipment' started by Richard Chambers, Feb 10, 2005.

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  1. Could you please recommend a book that would teach me the basics of RS-485
    and RS-422 ? I have been in the library, using the computer to attempt to
    find a book with RS-485 (or RS485, RS-422, RS422) in its title, but without
    success. When I searched for "data communications" instead, I found a number
    of books, but none of these had a section on RS-485 or RS-422, and they all
    had no relevance to what I wanted to know.

    Is there any difference between RS-485 and RS-422, or are they the same? Is
    RS-485 the same as the four-wire (i.e. two twisted pairs) version of
    ethernet, standard 802.3 ?

    I have four power station electrical meters. The data from these meters are
    tee-ed into a four-wire (two twisted pairs) RS-485 bus cabling system, which
    is interrogated by a RS-485 to RS-232 converter. I want to find out how the
    main interrogator can direct its interrogation first at meter 1, then at
    meter 2, etc. What sort of signals is the RS-232 to RS-485 converter
    putting onto the two sets of twisted pairs (that's all the wires we have) to
    specify and call up first meter 1, then meter 2, etc.? How does each meter
    "know" that it, and not one of the other meters, is being called upon to
    download its data?

    Richard Chambers Leeds UK.
  2. Joe Soap

    Joe Soap Guest

    In response to what Richard Chambers
    Useful info here:
  3. Since I haven't found a good book on the subject, might I suggest
    deriving the information from datasheets. I would suggest the datasheets
    for RS485 and 75176 as common interface devices, and SCC8530 ? for a
    controller IC. As you have probably deduced RS485 is a serial datacomms
    format similar to RS232 , the significant difference being the levels
    and the fact that it is multidrop(and so must have some sort of
    addressing scheme) and not point to point.

    Hope this helps

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