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RS 485 addressing — Parallax Forums

RS 485 addressing

GlennTGlennT Posts: 3
edited 2006-02-17 20:37 in BASIC Stamp
My company recently disposed of a few old data collection and control modules that communicate through RS-485.· The address of each seems to be set using dip switches.· Could someone explain to me how rs-485 addressing works esp. the hardware side?

Thanks
GlennT

Comments

  • Jon WilliamsJon Williams Posts: 6,491
    edited 2006-02-17 16:10
    RS-485 is a connection scheme -- it has no built in addressing (like I2C). Any addressing is used by the devices firmware and you'll need to find the documentation for it.

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    Jon Williams
    Applications Engineer, Parallax
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-02-17 20:37
    There's several approaches that could be taken.

    If you have 'dip' switches, then it's likely each 'node' (or board) had its switches set to give it a unique address. Then, in the firmware on the board, the processor 'listened' to the RS485 line. When it saw its address, it knew it was its turn to speak.

    This also implies a 'master' RS485 device on the bus, to tell each 'slave' address when to talk.

    But as Jon says, all of this is in firmware, it's not mandated by the standard.
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