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.
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:
| 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 |
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.
| Term | 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 |
