RS-485 and RS-422

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.

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Richard Chambers
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In response to what Richard Chambers posted in news:pJNOd.176$%

Useful info here:

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Joe Soap.
JUNK is stuff that you keep for 20 years,
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Reply to
Joe Soap

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


Reply to
Andrew Tweddle

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