Modbus Protocol¶
Table of Contents¶
Overview¶
Modbus is a widely used communication protocol in industrial automation. It operates on a master-slave architecture and supports data exchange between various industrial equipment.
Quick link¶
Related Protocols: SECS/GEM | EtherNet/IP | OPC UA | RTSP
Key Features¶
- Simplicity: Simple and easy-to-understand protocol structure
- Openness: Open standard supported by various vendors
- Reliability: Error detection and recovery capabilities
- Scalability: Usable in various network environments
Supported Functions¶
| Function | Description |
|---|---|
| Read Coils | Read digital output status |
| Read Discrete Inputs | Read digital input status |
| Read Holding Registers | Read holding registers |
| Read Input Registers | Read input registers |
| Write Single Coil | Write single coil |
| Write Single Register | Write single register |
| Write Multiple Coils | Write multiple coils |
| Write Multiple Registers | Write multiple registers |
Communication Methods¶
| Method | Description | Characteristics |
|---|---|---|
| Modbus RTU | Serial communication | Binary encoding, high efficiency |
| Modbus ASCII | Serial communication | ASCII encoding, easy debugging |
| Modbus TCP | Ethernet communication | TCP/IP based, high-speed communication |
Data Types¶
| Type | Description | Range |
|---|---|---|
| Coil | 1-bit read/write | 0 or 1 |
| Discrete Input | 1-bit read-only | 0 or 1 |
| Holding Register | 16-bit read/write | 0-65535 |
| Input Register | 16-bit read-only | 0-65535 |
Error Codes¶
| Code | Description |
|---|---|
| 01 | Illegal Function |
| 02 | Illegal Data Address |
| 03 | Illegal Data Value |
| 04 | Slave Device Failure |
| 05 | Acknowledge |
| 06 | Slave Device Busy |
| 08 | Memory Parity Error |
| 0A | Gateway Path Unavailable |
| 0B | Gateway Target Device Failed to Respond |