RESTful(ish) API to Modbus

Overview

REST service for allowing to read from Modbus TCP devices with different IP addresses or device IDs by making a REST call. Also allows to convert data to the desired data type and adjust data values through specifying an offset and multiplier.

At this stage only /read methods are supported.

API

Base URL: http://<serverIp>:20900/v1

Common path parameters in the API are:

• ip - IP of target device, such as 192.168.1.11.
• port - Modbus port, commonly 502.
• unitId - the slave ID as a numeric, commonly 1
• regType - The register type such as input, holding (supported).
• startAddress - the starting address of a read non incremented by 1.
• quantity - the number of registers to read.

URL	Method	Description
/read/{ip}/{port}/{unitId}/{regType}/{startAddress}/{quantity}/	GET	Reads the values of a register.
/random	GET	Test page to hit to check service.

Query Parameters

Conversion

The /read/... endpoint offers the transformation of the reading by providing conversion and endianness key value pair by appending the URL with ?conversion=raw. The following conversion are supported:

• conversion:
  • raw - Do not default to any conversion, always return raw response (default)
  • integer - Returns an integer representation of the register value
  • float32 - Interpret the input as a floating value according to IEEE-754.
• endianness:
  • little (default)
  • big

Offset and Multiplication

The /read/... endpoint offers the scaling of the reading by providing offset and multiplier key value pairs:

• offset (default 0)
• multiplier (default 1)

Example: http://localhost:20900/v1/read/192.168.255.1/502/1/holding/4110/1?offset=111&multiplier=0.1&conversion=raw&endianness=big

Acknowledgments

Code base from: https://github.com/pakerfeldt/node-modbus-rest