Modbus is a communication protocol for PLC Devices openly published by Modicon (now part of Schneider Electric). Since its publication in 1979 Modbus has been widely adopted as a communication protocol for PLC Devices and other types of device.
The Modbus Slave driver receives and processes requests from Modbus drivers in other products. The Modbus slave driver supports these variants of the Modbus protocol:
| Protocol | Description |
|---|---|
| Modbus RTU | 8-bit serial binary protocol |
| Modbus ASCII | 7 bit serial ASCII protocol |
| Modbus TCP | TCP/IP protocol |
The Modbus Slave Driver supports these Modbus commands:
| Command | Description |
|---|---|
| 01 | Read coil status |
| 02 | Read input status |
| 03 | Read holding registers |
| 04 | Read input registers |
| 05 | Force single coil |
| 06 | Preset single register |
| 08 | Diagnostics |
| 11 | Read comm event counter |
| 15 | Force multiple coils |
| 16 | Preset multiple registers |
| 17 | Report Slave ID |
| 22 | Mask Write Holding Register |
The Diagnostics Command (08) supports these sub-function values:
| Sub-Function | Description |
|---|---|
| 0 | Echo data |
| 1 | Restart communication |
| 2 | Return diagnostic register |
| 10 | Clear counters and diagnostic register |
| 11 | Return bus message count |
| 12 | Return bus communication error count (CRC) |
| 13 | Return bus exception error count |
| 14 | Return slave message count |
| 15 | Return slave no response count |
| 16 | Return slave NAK count |
| 17 | Return slave busy count |
| 18 | Return bus character overrun count |
The Modbus Slave driver provides these tag types to support communication using the Modbus protocol:
| Icon | Tag Type | Version | Description |
|---|---|---|---|
| Modbus Slave TCP Channel Tag | 3.10 | A TCP/IP Server allowing connections from Modbus drivers in other products. |
| Modbus Slave Serial Channel Tag | 3.10 | A serial port used to receive and process Modbus requests. |
| Modbus Slave Device | 3.10 | A virtual Modbus device. |
For a description of the Modbus Protocol.
For information about other drivers available in Fernhill SCADA.
For the meaning of terms used in Fernhill SCADA.