Extend modbus support

Let the user decide which parity/stop bit configuration is used eg. even/odd parity and one stop bit or just two stop bits.
(like the async serial analyzer does)

Support extended 16-bit slave addresses
(Yes, it's not a de facto standard, but it's still widely used in bigger modbus networks. Also it should be easy to implement)


  • Lars
  • Jul 11 2018
  • klaas commented
    July 11, 2018 21:04

    I agree to Mark Garrisson. If you are on RS-485, TX and RX are on the same wire. The slave has to reply to each master command. The current decoder will see the slave answer as a new master command and will decode rubbish.

    Saleae's Modbus RTU decoding support on RS-485 thus is unusable: we need a new option that master and slave are intermixed.

  • Mark Garrison commented
    July 11, 2018 21:04

    The analyzer should also support decoding master and slave messages from the same input, at the same time.
    Currently the analyzer requires TX and RX signals to be recorded separately on different inputs before they reach a RS-485 transceiver.
    This would allow the analyzer to decode all traffic on the bus by directly probing the bus.

  • Jamie commented
    July 11, 2018 21:04

    I purchased the Saleae Logic because it was one of the few low cost analyses that supported the modbus protocol which is used in several of our products. Unfortunately not being able to set the parity/stop bit configuration make the current implementation practically useless.

    As Lars suggests if the same settings as the async serial could be applied to the modbus protocol, it would make it infinitely more usable.