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.
The terminology Master and Slaves refers to outdated terms. The Modbus Organization announced the replacement of "master-slave" terminology with "client-server" in its communications protocol. The new nomenclature reflects the specific roles of the devices within the Modbus network. Here's a clearer explanation:
On this page:
Modbus Master (Client): In the context of the Modbus protocol, the "master" is the device that initiates communications. It’s called a Client because it requests data from other devices. The master actively controls when and how data is requested and collected in the network.
Modbus Slave (Server): Slave devices are referred to as Servers because they serve data to the master upon request. They passively wait for requests and respond by sending the requested data or performing actions based on the commands received. They do not initiate communication; they only respond to the master’s requests.
Summary
Modbus Server driver implements communication with Client devices compatibles with Modbus Open Standard protocol. It operates as a Server on TCP/IP or serial networks.
Communication Driver Information | |
|---|---|
Driver name | Modbus Server |
Assembly Name | T.ProtocolDriver.ModbusSlave |
Assembly Version | 2.0.0.8 |
Available for Linux | False |
Devices supported | Any Client 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 Client 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 Server 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.
You may need to configure your firewall to open the listening port. |
Nodes Configuration
Station Configuration
There is no station configuration for the Modbus Server 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 | SERVER DEVICE FAILURE | Error while attempting to perform the requested action. |
5 | ACKNOWLEDGE | Request accepted, but a long duration of time will be required. |
6 | SERVER DEVICE BUSY | The server 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
ModbusServer Revision History | |
|---|---|
Version | Notes |
2.0.0.7 | Initial release on new documentation standards. |