This document has only the specific information about the device connection settings and its address syntax.

Refer to the User Guide for more information on the  Device Module.

Summary

Modbus Slave driver implements communication with master devices compatibles with Modbus Open Standard protocol. It operates as a Slave on TCP/IP or serial networks.

Communication Driver Information

Driver name

ModbusSlave

Assembly Name

T.ProtocolDriver.ModbusSlave

Assembly Version

2.0.0.8

Available for Linux

False

Devices supported 

Any master Modbus device

Manufacturer

N/A (Not Applicable)

Protocol

MODBUS RTU, ASCII and TCP

Interface

TCP/IP and Serial

Protocol Options

Message Format (ASCII, RTU or RTU TCP), SlaveID

Multi-threading

One thread with a pooling cycle for each master connected

Max number of nodes

One node for each channel

PC Requirements

Standard PC Ethernet interface board, RS485 or RS232 port

Supported Operands

Operand

Read

Write

Data Type

Address size

0 – Coils

Yes

Yes

Bit

1 bit

1 – Input Status

Yes

-

Bit

1 bit

3 – Input Registers

Yes

-

Word

2 bytes

4 – Holding Registers

Yes

Yes

Word

2 bytes

Channels Configuration

Protocol Options

  • SlaveID: Defines the driver slave address in the Modbus Network.
  • Encoding:  Determines how the information will be packed into the message fields and decoded. The options are:
    • RTU: Remote Terminal Unit mode, where each 8–bit byte in a message contains two 4–bit hexadecimal characters
    • ASCII: The message is encoded in ASCII mode, where each 8–bit byte in a message is sent as two ASCII characters
    • RTU TCP: The default transmission mode when the message is carried on a MODBUS TCP/IP network. It contains information to allow the recipient to recognize message boundaries even if the message has been split into multiple packets

Settings

Serial and MultiSerial channels:

  • Default configuration for ASCII mode :
    • DataBits: 7
    • StopBits: 1 if parity is used, 2 if no parity
  • Default configuration for RTU mode :
    • DataBits: 8
    • StopBits: 1 if parity is used, 2 if no parity


Set the other fields according to your Serial or MultiSerial port configuration

TCP/IP channels:

  • Listening Port: Defines the TCP port where the driver will be listening for the connections, the default TCP port for the Modbus Network is 502.


NOTE

You may need to configure your firewall to open the listening port.

Nodes Configuration

Station Configuration 

There is no station configuration for the Modbus Slave driver.


Point Configuration

The syntax for the Modbus communication points is: <Operand><Address>

Where:

  • <Operand>: indicates the memory area
  •  <Address>: indicates the data address in the memory area, from 1 to 65535

Valid values for <Operand>

0 – Coils

1 – Input Status

3 – Input Registers

4 – Holding Registers

For more information about the valid operands, see the Supported Operands table aforementioned.


E.g.: 400001 (Operand = Holding Register, Address = 1)


Troubleshoot

Modbus protocol error codes

Error

Name

Description

1

ILLEGAL FUNCTION

The function code received in the query is not allowable.

2

ILLEGAL DATA ADDRESS

The data address received in the query is not allowable.

3

ILLEGAL DATA VALUE

A value contained in the query data field is not allowable.

4

SLAVE DEVICE FAILURE

Error while attempting to perform the requested action.

5

ACKNOWLEDGE

Request accepted, but a long duration of time will be required.

6

SLAVE DEVICE BUSY

The slave is engaged in a long–duration program command.

7

NEGATIVE ACKNOWLEDGE

Cannot perform the program function received in the query.

8

MEMORY PARITY ERROR

Parity error in the extended memory.

Driver Revision History

ModbusSlave Revision History

Version 

Notes

2.0.0.7

Initial release on new documentation standards.

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