MyEMS Modbus TCP Service

Introduction

This service is a component of MyEMS to acquire data from Modbus TCP devices.

Prerequisites

pyserial

modbus-tk

mysql.connector

Installation

Download and install MySQL Connector:

    $ cd ~/tools
    $ wget https://dev.mysql.com/get/Downloads/Connector-Python/mysql-connector-python-8.0.20.tar.gz
    $ tar xzf mysql-connector-python-8.0.20.tar.gz
    $ cd ~/tools/mysql-connector-python-8.0.20
    $ sudo python3 setup.py install

Download and install modbus-tk

    $ cd ~/tools
    $ git clone https://github.com/pyserial/pyserial.git
    $ cd ~/tools/pyserial
    $ sudo python3 setup.py install
    $ git clone https://github.com/ljean/modbus-tk.git
    $ cd ~/tools/modbus-tk
    $ sudo python3 setup.py install

Install myems-modbus-tcp service

    $ cd ~
    $ git clone https://github.com/MyEMS/myems.git
    $ cd myems
    $ sudo git checkout master (or the latest release tag)
    $ sudo cp -R ~/myems/myems-modbus-tcp /myems-modbus-tcp

Eidt the config

    $ sudo nano /myems-modbus-tcp/config.py

Setup systemd service:

    $ sudo cp /myems-modbus-tcp/myems-modbus-tcp.service /lib/systemd/system/
    $ sudo systemctl enable myems-modbus-tcp.service
    $ sudo systemctl start myems-modbus-tcp.service

Add Data Sources and Points in MyEMS Admin

NOTE: If you modified Modbus TCP datasources and points, please restart this service:

    $ sudo systemctl restart myems-modbus-tcp.service

Input Data source protocol:

modbus-tcp

Data source connection example:

{"host":"10.9.67.99","port":502}

Point address example:

{"slave_id":1, "function_code":3, "offset":0, "number_of_registers":2, "format":"<f", "byte_swap":true}

Address

slave_id

The slave ID

function_code

01 (0x01) Read Coils
02 (0x02) Read Discrete Inputs
03 (0x03) Read Holding Registers
04 (0x04) Read Input Registers
23 (0x17) Read/Write Multiple registers

offset

The starting register address specified in the Request PDU

number_of_registers

The number of registers specified in the Request PDU

format

Use python3 library struct to format bytes. Python bytes objects are used to hold the data representing the C struct and also as format strings (explained below) to describe the layout of data in the C struct.

The optional first format char indicates byte order, size and alignment: @: native order, size & alignment (default) =: native order, std. size & alignment <: little-endian, std. size & alignment >: big-endian, std. size & alignment !: same as >

The remaining chars indicate types of args and must match exactly; these can be preceded by a decimal repeat count: x: pad byte (no data); c:char; b:signed byte; B:unsigned byte; ?: _Bool (requires C99; if not available, char is used instead) h:short; H:unsigned short; i:int; I:unsigned int; l:long; L:unsigned long; f:float; d:double.

Special cases (preceding decimal count indicates length): s:string (array of char); p: pascal string (with count byte). Special cases (only available in native format): n:ssize_t; N:size_t; P:an integer type that is wide enough to hold a pointer.

Special case (not in native mode unless 'long long' in platform C): q:long long; Q:unsigned long long

Whitespace between formats is ignored.

byte_swap

A boolean indicates whether or not to swap adjacent bytes.
Swap adjacent bytes of 32bits(4bytes) or 64bits(8bytes). This is not for little-endian and big-endian swapping, and use format for that. The option is effective when number_of_registers is ether 2(32bits) or 4(64bits), else it will be ignored.

References

[1]. http://myems.io

[2]. http://www.modbus.org/tech.php

[3]. https://github.com/ljean/modbus-tk

[4]. https://docs.python.org/3/library/struct.html#format-strings