ENMAT Help Desk > ENMAT Support Help Desk > Knowledgebase

Ask a question:



ENMAT_MODBUSModbus enables communication among many (approximately 240) devices connected to the same network. Modbus is now used by many manufacturers for instrument and control communications.

ENMAT Smart Meters using the Modbus protocol use the RTU (Remote Terminal Unit) mode and CRC (not LRC) error checking, with all Meters acting as Slaves. An ENMAT Data Logger will act as a MODBUS Master, initiating communication with the meters and centralising the data into the internet enabled data logger. From there the data is sent to ENMAT Cloud Software via an internet connection.

In Modbus RTU, bytes are sent consecutively with no space in between them with a 3-1/2 character space between messages for a delimiter.  This allows the software to know when a new message is starting.

Each device intended to communicate using Modbus is given a unique address.

Communication on a MODBUS Network is initiated (started) by a “Master” with a “query” to a “Slave”.

The“Slave “ which is constantly monitoring the network for “Queries” will recognise only the “Queries”
addressed to it and will respond either by performing an action (setting a value for example) or by
returning a “response”. Only the Master can initiate a query.

RS485 is the hardware specification for the physical wiring and connections. Modbus is the protocol
specification that each device uses to communicate over the RS485 serial line.Modbus is a protocol
specification designed for building automation equipment used to interface with various devices over RS485 serial, and TCP/IP interfaces.

A serial hardware specification that most modbus devices communicate over.

Modbus/485 loops may be up to 4000ft. Your results may vary depending on the quality of the wire,
electrical noise, and the modbus devices attached to the loop. Modbus repeaters may be used to extend the length of the loop, but introduce delay in the device response time. Using repeaters on slow devices may cause timeout problems.

Daisy chain the devices together. Do not use ‘spur’ lines, or a star configuration. Terminating Resistors of 120 Ohms should be used on the ends of long modbus/485 loops.









A modbus map is simply a list for an individual slave device that definesTwisted Pair is required. Short runs can be 24 gauge wire, unshielded. Longer runs (+100ft) should use 18
gauge wire with shield. Shielded twisted pair should also be used if electrical noise is present, from motors,
relays, etc. When running the modbus loop into a breaker panel, one must observe the voltage present in the panel and use wire with appropriate insulation.

- what the data is (eg. kWh or temperature readings)
- where the data is stored (which tables and data addresses)
- how the data is stored (data types, byte and word ordering)

Some devices are built with a fixed map that is defined by the manufacturer. While other devices allow the operator to configure or program a custom map to fit their needs.

Was this article helpful? yes / no
Article details
Article ID: 61
Category: Technical Articles
Date added: 2014-04-24 15:17:44
Rating (Votes): Article rated 3.4/5.0 (20)

« Go back

© ENMAT - Envantage Ltd