RS485 on rPi

[last updated: 2022-10-10]
RS485 home page
rPi serial communication
see also GMC GUI project
rPi home page
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• Connect rPi to MAX485 module:
  • The rPi communicates to the MAX485 module with serial communication (using an onboard UART).
    rPi serial port (UART0) uses GPIO14 (Tx) and GPIO15 (Rx)

• Connections:
  There are five connections required between the rPi and the MAX module.
  • +5v and gnd to power the MAX485
        (strictly speaking the MAX could be powered with a separate supply instead of from the rPi,
        but the gnd connection between them is still required.)
  • 3 signal connections:
    rPi digital output -to- MAX-DE/RE: allow the rPi to control the MAX's enable line (High to Tx, Low to Rx)
    rPi-Tx -to- MAX-DI: serial data sent from the rPi to the MAX module
    MAX-RO -to- rPi-Rx: serial data received by the MAX485 on its RS485 bus, and sent to the rPi Rx receive pin
    
  • The enable control and the rPi-Tx signals can be directly connected to the MAX485,
    because the 3.3v output from the rPi will still be read as digital high on the 5v MAX485.
  • However the 5v RO signal sent from the MAX485 would damage the 3.3v inputs on the rPi if it were directly connected,
    so a level shift circuit is required.

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• Links:
  • https://forums.raspberrypi.com/viewtopic.php?t=204305

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