RS485 bus voltage ?? Can you mix nodes using 3/3v and 5v transceivers ?



  • I am working on setting up a my sensors network consisting of both wired (using RS485) and wireless (NRF or ESP) nodes..

    I just added a sc16is752 to my RPI3 for some much needed additional serial interfaces and am now looking at using those interfaces for RS485. 1 for the RS485 my sensors bus and the other as a modbus interace to mu power monitoring device.

    I grabbed a max485, realized it's a 5v device.. and then it hit me..

    I can either use a level converter or look for a 3.3v rs485 transceiver.. no issue there, that's only local.. But the rs485 bus is meant for many devices..

    What about the rs485 bus voltage ? it has no pull-ups, only the 120ohm terminators on both sides.. but what voltage does it use ?

    Can you run a rs485 bus between devices equiped with rs485 transceiver using a mixed supply voltage of 3.3v and 5v ?


  • Mod

    @Redguy from http://m.electronicdesign.com/what-s-difference-between/what-s-difference-between-rs-232-and-rs-485-serial-interfaces: "A logic 1 is a level greater than –200 mV, and a logic 0 is a level greater than +200 mV. Typical line voltage levels from the line drivers are a minimum of ±1.5 V to a maximum of about ±6 V. "

    So you should be able to mix them as much as you like.


 

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