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Awesome Open Source

ModbusRestAPI

A service that exposes the Modbus protocol via a RESTful API. The service was built using C# and Mono so it should work in all platforms. If curious what Modbus is, please check (http://www.minaandrawos.com/2014/11/26/how-to-write-a-modbus-driver/#WhatIsModbus ). Happy hacking!!

The API is as follows:

  • Post: /Read/{deviceType}:

    • Task: Reads a number of Modbus registers. The {devicetype} could be either "coils", "holdingregisters", "inputregisters", or "inputs"
    • Body: The body will follow the format below
            {
              "destination": "ip:portnumber or serial address",
              "connectiontype": 0 for serial RTU, 1 for serial ASCII, or 2 for TCP,
              "slaveid": slave address as a number,
              "address": offset number where we want to start the reads,
              "count": number of registers to read
            }
    

    For example, let's say we want to connect to Modbus TCP, the device TCP address is "10.1.1.1:502", the connection is TCP obviously, the slave id is 1, and we want to read starting from register address 1414 for five registers. Here is how the request will look like:

            {
              "destination": "10.1.1.1:502",
              "connectiontype": 2,
              "slaveid": 1,
              "address": 1414,
              "count": 5
            }
    
  • Post: /Write/{devicetype}:

    • Task: Perform a write to a Modbus register. The {devicetype} could be either coils or holdingregisters
    • Body: The body will follow the format below:
            {
              "destination": "ip:portnumber or serial address",
              "connectiontype": 0 for serial RTU, 1 for serial ASCII, or 2 for TCP,
              "slaveid": slave address as a number,
              "address": register offset number where we want to start the reads,
              "data": the data to write to the device. This will either be an array of bools or ushorts
            }
    

    For example, let's say we want to connect to Modbus TCP, the device TCP address is "10.1.1.1:502", the connection is TCP as well, the slave id is 1, we want to write to holding registers starting from register address 1414 values [14,21,12]. The request will go to /Write/holdingregisters:

            {
              "destination": "10.1.1.1:502",
              "connectiontype": 2,
              "slaveid": 1,
              "address": 1414,
              "data": [14,21,12]
            }
    

The service uses Nancy(http://nancyfx.org) for the web layer, and NModbus4 (https://awesomeopensource.com/project/NModbus4/NModbus4) for the Modbus layer. The service makes use of Nancy's self hosting capabilities so the API is self hosted.

The code in theory should support Holding registers, Input registers, Coils, and Inputs. It should also support Modbus TCP, Serial RTU and serial ASCII. However, I don't have enough devices to test all these modes.

The service and the code are provided as is. You are free to use and refactor the code but do so at your own risk. Please include my name as the original author of the code.


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