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I am using an rs422 driver and receiver IC for connecting 2 different boards. Now I have seen many circuits of rs422 which have passives connected in them. Why is that ? And how are they calculated ? The precise values of resistors and capacitors.

What is the need for such passives please ?

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  • \$\begingroup\$ Both your RS422 questions, which if they were of sufficient quality could have been combined to spare clutter, are very easily researched with Google, by typing... "RS422" for a start. Yet you show no effort taken in either of them. \$\endgroup\$ – Asmyldof Oct 29 '15 at 7:33
  • \$\begingroup\$ Thank u for ur wise comments. If someone asks all doubts in 1 post down vote saying put them in diff posts. If put in diff posts merge it. \$\endgroup\$ – Board-Man Oct 29 '15 at 7:38
  • \$\begingroup\$ @Asmyldof Splitting different questions into different posts is the correct way to do it. Especially in this case, since bus termination and ESD concerns are not really related topics. \$\endgroup\$ – Lundin Oct 29 '15 at 8:01
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The resistor on receiver side is a termination resistor. Think the output driver as a current source driving a negative or positive current over the termination. The receiver senses the polarity of the voltage caused by the current. You can add caps as well for an AC termination.

Here's a TI document (SLLA070D) that describes the different terminations.

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