Electroswitch 25-1000 - Serial Communications

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25-1000-UM 11

SERIAL COMMUNICATION

Modbus Protocol

This section describes the Modbus communications protocol of the 25-1000 Series Arga Battery Monitor

(ABM), and how to exchange information with the ABM switch utilizing the Modbus protocol. The ABM Series

communicates by emulating a subset of the Modbus protocol in the operational software of the Lockout

Relay. Modbus communications uses a Master-Slave technique in which only the master can initiate a

transaction. This transaction is called a ‘Query’. When appropriate, a slave responds to the query. When a

master communicates with a slave, information is provided or requested by the master. When a slave device

receives a query, the slave responds by either supplying the requested data to the master or performing the

requested action. A slave device never initiates communications on the Modbus network, and will always

generate a response to the query addressed to it unless certain error conditions occur. The ABM Series is

designed to operate only as slave device.

Device Address

The Device Address contains the unique Modbus address of the slave being queried. Modbus protocol limits a device

address from 0 to 247 and even though addresses beyond this range can be selected they will be ignored. Address 0 is

the broadcast address but not all functions support "broadcast". The address and baud rate are user selectable in the

SYS menu.

Function Code

The Function Code in the query message defines the action to be taken by the addressed slave.

The Arga battery monitor stores user input information into holding register address space in the following

order fault alarms, battery voltage, fault voltage, minus ground voltage, ripple voltage, and ripple current.

They start at the programmed first register location. This device supports the following function codes;

Function 03 (03h) – Read Holding Registers – Used to read the measurements of the meter.

Function 05 (04h) – Read Input Registers – Used to read the measurements of the meter.

Function 08 (08h) – Diagnostic Sub function 0 – Used to test the relay.

Alarms Bit Description

Point

Index

Name/Description Change Event Class (1, 2, 3 or none)

0 High Battery Alarm (1 = Alarm) 1

1 Low Battery Alarm (1 = Alarm) 1

2 Plus Ground Fault Alarm (1 = Alarm) 1

3 Minus Ground Fault Alarm (1 = Alarm) 1

4 Ripple Voltage Alarm (1 = Alarm) 1

5 Ripple Current Alarm (1 = Alarm) 1

6 AC Power Fail Fault Alarm (1 = Alarm) 1

7 High Impedance Alarm (1 = Alarm) 1