Custom Modbus Registers

Custom Modbus Registers

Introduction

Modbus is a protocol created to transmit signals between electronic devices over serial communication lines. It has gained widespread popularity in industrial automation and manufacturing due to its open source standard and reliability.

In an industrial setting there is usually a master controller such as a PLC that speaks to all other devices in the network to retrieve or write data. These devices can be sensors, energy meters, pressure values or other slave devices.

A Modbus map provides a structured process to identify and fetch data from memory blocks from a slave device. Information is typically store in different tables categorized as coils, discrete inputs, input registers or holding registers.

The master does sends out a request to a specific slave device such as a meter or controller. When it receives a response from one of the slave device it sends out a function code containing the register start address and the number of blocks it should access.

Regular Modbus Registers

Modern operators familiar with this method of data extraction are quick to realize how inefficient this method really is. Instead of pulling only the register addresses it requires, the entire block sequence is returned for the master to process and filter.

Acuvim II series meters have 64 configurable Modbus registers included in the meter which can be selected by users for a customized sequence of existing metering parameters.

What is this used for / why?

The custom Modbus register list in addition to the existing registers allows users and integrators to optimize Modbus polling for their unique requirements. The ability to set a unique register list/sequence means when meters are polled via Modbus software the master can be configured more efficiently to only receive the necessary information for a faster response time.

Custom Modbus Registers

Efficient

The Acuvim II series meters are designed to be flexible and powerful enough to work in a large variety of applications, and as such have over 400 unique measurement parameters, however in many of the applications only 20 or less parameters are typically used at one time.

Faster Responses

In Modbus a master device in unable to request specific registers to poll causing all registered blocks between the two points to be returned. Having excess registers creates an additional process that needs to be undertaken by the master to find and extract the relevant data, but by using custom Modbus registers to limit the polled registers to the specific information needed means less time is spent filtering the data while more information can be processed.

Benefits/Outcomes

  • Select Register Type – registers can be configured as float, integer, or double word
  • Optimized Data – Select only the data you wish to read
  • More efficient processes – all the information is selected in one poll

Enabling Custom Modbus Registers

With the web server interface users can easily configure the custom register list.

AXM-WEB2  WiFi & Dual Ethernet Communication Module
Specially designed for fast and reliable data transmission using AXM-WEB2 built-in dual Ethernet ports and WiFi communication channels for the Acuvim II power & energy meter. Supports a wide range of protocols such as Modbus-TCP/IP, sFTP, BACnet-IP, DNP3 V2 and IEC61850 2nd edition.