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RS422 to RS485 connection

I have an RS422 card in my PC which I would like to use to control a Siemens CPU216 PLC.  The PLC comms port is RS485.  What I would like to know are the DB9 pin connections for making a cable between the two.  I imagine that it would be easy, but it's Friday afternoon and I can't see it.  :o(
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A__Smith
Asked:
A__Smith
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1 Solution
 
j2Commented:
Stop, Cease!

Do NOT do that, you _WILL_ fry the RS232 board.

You MUST purchase a rs232 <-> rs485 converter, or a RS485 card for your PC.
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j2Commented:
something like this

http://www.rs485.com/rsfc24.gif
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j2Commented:
j2 changed the proposed answer to a comment
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j2Commented:
Ok, stupid me read that wrong, thought you said you had a 232 in your computer

you need this
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j2Commented:
Ok, stupid me read that wrong, thought you said you had a 232 in your computer

you need this

http://www.rs485.com/pdiacr44.html

or this

http://www.rs485.com/pdisodin.html
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gdelbruyereCommented:
1) I know different RS422/485 cards that have differents pinouts.

2) a) RS 422 is basicly a One to One link that can be extented to a One-Speaker to severall Receiver system.  In fact, take a usual 232 link, switch it to a balanced electrical  signal, and you'll get Some thing like 422 which has 2*2 wires.
  In addition, you can have severall listenners on each of the two pairs of lines... But only one speaker per peer.  

b) RS485 is a Multi Speaker and Receiver sheme.
To get this, the only solution is one Bus (which here is only a dual wire with balanced signal), to which all speakers must talk, and listen too.
Due to that the 485 is half duplex, (usually solved by a master whicj polls  
the others to simulate a kind of token)

c) at an electrical point of view (if few node and short line length)  switching fron 422 to 485 is only shortcutting sending and receiving lines (+toegether and - toegether) on the card.
BUT THE SOFTWARE MUST ALLOW IT (using an Half Duplex sheme and 'forgetting its own echoed  
messages.AND SETTING the Output in a high impedance when listenning !! )

If So,  here are the pinouts of two cards I know

         DB25        DB9
TD+      2              3  
RD+      3              2
TD-     14              4
RD-     15              1
   



Guy
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A__SmithAuthor Commented:
Thanks for the scare, j2.  ;o)  Thanks for the answer, too; that's a better solution for me than mere line swapping within a cable.

Thanks also to Guy.
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