Notes on Lollette LE3U PLC

Raspberry Pi connected to Lollette LE3U
Raspberry Pi connected to Lollette LE3U over Modbus RTU (RS485).
  • Lollette LE3U is a “copy” of the Mitsubishi FX3U PLC for $60 on AliExpress while the original costs around $1000.
  • All configuration is done using Mitsubishi’s proprietary software GX Developer or GX Works2 which cost another $500 but have a 60-day free trial available online.
  • It features 14 digital inputs, 6 analog inputs, 2 analog output and 10 relay outputs.
  • The RS485 port is not configured by default so you can’t control any of the relays or read input values without first uploading new configuration program.
  • Programming is done using visual Ladder language which is somewhat confusing to get started until you realise that it’s pretty much a mapping of input triggers, registers and their values.
    • Each physical input maps to a register which can then change another output register depending on certain rules.
    • Configuring parameters is “moving” 1-byte or 2-byte strings into registers.

Configure RS485 Modbus

To configure the device as a Modbus “slave”, hook into the M8002 event and configure the following registers:

  • D8120 with the details for the serial protocol. Set it to H4081 to enable Modbus RTU slave protocol with 8 data bits, 0 parity bits, 1 stop bit and a 9600bps transfer rate.
  • D8121 for the device ID or station number. Set to K1 where 1 is the device ID.
  • D8129 for the communication timeout (optional). Set to K100 where 100 is the timeout in milliseconds.

The 4-byte values are entered as a string of matching hex values starting from the lowest bit (please ignore the actual register values since this is from a different device):

Example of register value bit mapping to H notation.

See these two videos for detailed instructions:

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