Top 10 RS-485 design tips

At TI, we often get questions about whether there are any quick tips or tricks to keep in mind when designing with RS-485. So, we've put together a comprehensive list of the top commandments to remember when working with RS-485. If you have any further questions on this topic, our team is always hanging out on our E2E forum, and we would be happy to help. So, without further ado...

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How to apply them...

1) Determine maximum cable length with Chart A

2) Use twisted pair cable with Zo = 120Ω or 100Ω

3) Connect bus nodes via daisy chain

4) Terminate one cable end with RT1 = Z0

    Apply failsafe biasing to the other end 

    Terminate this end 

5) You can operate 3V and 5V devices on the same bus

6) Make stub length no longer than 

7) For ± 7V GPDs use standard transceivers

       For ± 20V GPDs use SN65HVD17xx

       For higher GPDs use isolated transceivers 

8) Terminate unused conductors with RT = Z0 to their local grounds

9) For ESD, EFT, and surge protection use SM712

10) Limit clamping current into the transceiver with 10-Ω pulse-proof or MELF resistors

Do you have your own tips? Share them with our readers below.


Learn more about TI's RS-485 transceivers, drivers, receivers and other ICs.

Have more questions? Ask them on TI's E2E Industrial Interface Forum.

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