Version 2.0.0rc1

Note This is a Major release and might affect your existing Async client implementation. Refer examples on how to use the latest async clients.

  • Async client implementation based on Tornado, Twisted and asyncio

Version 1.5.1

  • Fix device information selectors

  • Fixed behaviour of the MEI device information command as a server when an invalid object_id is provided by an external client.

  • Add support for repeated MEI device information Object IDs (client/server)

  • Added support for encoding device information when it requires more than one PDU to pack.

  • Added REPR statements for all syncchronous clients

  • Added isError method to exceptions, Any response received can be tested for success before proceeding.

    ``` res = client.read_holding_registers(…) if not res.isError():

    # proceed


    # handle error or raise


  • Add examples for MEI read device information request

Version 1.5.0

  • Improve transaction speeds for sync clients (RTU/ASCII), now retry on empty happens only when retry_on_empty kwarg is passed to client during intialization

client = Client(…, retry_on_empty=True)

  • Fix tcp servers (sync/async) not processing requests with transaction id > 255
  • Introduce new api to check if the received response is an error or not (response.isError())
  • Move timing logic to framers so that irrespective of client, correct timing logics are followed.
  • Move framers from to respective modules
  • Fix modbus payload builder and decoder
  • Async servers can now have an option to defer when using Start<Tcp/Serial/Udo>Server(…,defer_reactor_run=True)
  • Fix UDP client issue while handling MEI messages (ReadDeviceInformationRequest)
  • Add expected response lengths for WriteMultipleCoilRequest and WriteMultipleRegisterRequest
  • Fix _rtu_byte_count_pos for GetCommEventLogResponse
  • Add support for repeated MEI device information Object IDs
  • Fix struct errors while decoding stray response
  • Modbus read retries works only when empty/no message is received
  • Change test runner from nosetest to pytest
  • Fix Misc examples

>>>>>>> master

Version 1.4.0

  • Bug fix Modbus TCP client reading incomplete data
  • Check for slave unit id before processing the request for serial clients
  • Bug fix serial servers with Modbus Binary Framer
  • Bug fix header size for ModbusBinaryFramer
  • Bug fix payload decoder with endian Little
  • Payload builder and decoder can now deal with the wordorder as well of 32/64 bit data.
  • Support Database slave contexts (SqlStore and RedisStore)
  • Custom handlers could be passed to Modbus TCP servers
  • Asynchronous Server could now be stopped when running on a seperate thread (StopServer)
  • Signal handlers on Asyncronous servers are now handled based on current thread
  • Registers in Database datastore could now be read from remote clients
  • Fix examples in contrib (
  • Add new example for SqlStore and RedisStore (db store slave context)
  • Fix minor comaptibility issues with utilities.
  • Update test requirements
  • Update/Add new unit tests
  • Move twisted requirements to extra so that it is not installed by default on pymodbus installtion

Version 1.3.2

  • ModbusSerialServer could now be stopped when running on a seperate thread.
  • Fix issue with server and client where in the frame buffer had values from previous unsuccesful transaction
  • Fix response length calculation for ModbusASCII protocol
  • Fix response length calculation ReportSlaveIdResponse, DiagnosticStatusResponse
  • Fix never ending transaction case when response is recieved without header and CRC
  • Fix tests

Version 1.3.1

  • Recall socket recv until get a complete response
  • Observe skip_encode option when encoding a single register request
  • Fix wrong expected response length for coils and discrete inputs
  • Fix decode errors with ReadDeviceInformationRequest and ReportSlaveIdRequest on Python3
  • Move MaskWriteRegisterRequest/MaskWriteRegisterResponse to from
  • Python3 compatible examples [WIP]
  • Misc updates with examples

Version 1.3.0.rc2

  • Fix encoding problem for ReadDeviceInformationRequest method on python3
  • Fix problem with the usage of ord in python3 while cleaning up receive buffer
  • Fix struct unpack errors with BinaryPayloadDecoder on python3 - string vs bytestring error
  • Calculate expected response size for ReadWriteMultipleRegistersRequest
  • Enhancement for ModbusTcpClient, ModbusTcpClient can now accept connection timeout as one of the parameter
  • Misc updates

Version 1.3.0.rc1

  • Timing improvements over MODBUS Serial interface
  • Modbus RTU use 3.5 char silence before and after transactions
  • Bug fix on FifoTransactionManager , flush stray data before transaction
  • Update repository information
  • Added ability to ignore missing slaves
  • Added ability to revert to ZeroMode
  • Passed a number of extra options through the stack
  • Fixed documenation and added a number of examples

Version 1.2.0

  • Reworking the transaction managers to be more explicit and to handle modbus RTU over TCP.
  • Adding examples for a number of unique requested use cases
  • Allow RTU framers to fail fast instead of staying at fault
  • Working on datastore saving and loading

Version 1.1.0

  • Fixing memory leak in clients and servers (removed __del__)
  • Adding the ability to override the client framers
  • Working on web page api and GUI
  • Moving examples and extra code to contrib sections
  • Adding more documentation

Version 1.0.0

  • Adding support for payload builders to form complex encoding and decoding of messages.
  • Adding BCD and binary payload builders
  • Adding support for pydev
  • Cleaning up the build tools
  • Adding a message encoding generator for testing.
  • Now passing kwargs to base of PDU so arguments can be used correctly at all levels of the protocol.
  • A number of bug fixes (see bug tracker and commit messages)

Version 0.9.0

Please view the git commit log