The Modbus Slave driver implements communication with Master devices compatible with the Modbus Open Standard protocol. It operates as a Slave on TCP/IP or serial networks.

Summary Information

Communication Driver Name: Modbus Slave

Implementation DLL: T.ProtocolDriver.ModbusSlave.dll

Protocol: MODBUS RTU, ASCII, and TCP

Interface: TCP/IP and Serial

Devices supported: Any master Modbus device

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 Hardware requirements: Standard PC Ethernet interface board, RS485, or RS232 port

Supported Operands:

Channel Configuration

Protocol Options

SlaveID: Defines the driver's slave address in the Modbus Network

Encoding: Determines how information will be packed into the message fields and decoded. The options are:

• RTU = Remote Terminal Unit mode. In a message, each 8–bit byte contains two 4–bit hexadecimal characters
• ASCII = The message is encoded in ASCII mode. Each 8–bit byte 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 that allows 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 listens for the connections. The default TCP port for the Modbus Network is 502

Node 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. The valid values are:
  • 0 for Coils
  • 1 for Input Status
  • 3 for Input Registers
  • 4 for Holding Registers

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

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

Ex: 400001 (Operand = Holding Register, Address = 1)

Troubleshoot

The status of the driver's execution can be observed through the diagnostic tools, which are:

• Trace window
• Property Watch
• Module Information

The above tools indicate if the operations have succeeded or have failed. A status of 0 (zero) means communication is successful. Negative values indicate internal driver errors, and positive values indicate protocol error codes.