1. Overview
The Siemens G120 VFD supports Modbus RTU communication through its RS485 interface. Based on Siemens' official technical documentation, this article explains the Modbus register address mapping of the G120 VFD in detail.
2. Modbus Communication Parameters
| Parameter No. | Parameter Name | Description |
|---|
| P2010 | USS/Modbus baud rate | Sets the communication baud rate |
| P2021 | USS/Modbus address | Sets the slave address (1-255) |
| P2023 | Protocol selection | Selects the Modbus RTU protocol |
3. G120 Modbus Register Mapping Table
3.1 Control Word and Status Word
| Modbus Address | Parameter No. | Description | Read/Write |
|---|
| 40001 | STW1 | Control word 1 | Write |
| 40002 | HSW | Main setpoint (frequency) | Write |
| 40003 | ZSW1 | Status word 1 | Read |
| 40004 | HIW | Main actual value (frequency) | Read |
3.2 Common Monitoring Parameters
| Modbus Address | Parameter No. | Description |
|---|
| 40021 | r0027 | Output current |
| 40022 | r0025 | Output voltage |
| 40023 | r0026 | DC bus voltage |
| 40024 | r0037 | Motor temperature |
4. Control Word Bit Definition
| Bit | Function | Description |
|---|
| 0 | ON/OFF1 | 1 = Start, 0 = Stop |
| 1 | OFF2 | 1 = Coast stop permitted |
| 2 | OFF3 | 1 = Fast stop permitted |
| 3 | Pulse enable | 1 = Enable the ramp function generator |
| 7 | Acknowledge fault | Acknowledges the fault on the rising edge |
| 11 | Setpoint acknowledge | 1 = Setpoint takes effect |
5. FAQ and Troubleshooting
- Check whether P2023 (protocol selection) is set to Modbus RTU
- Confirm that the slave address and baud rate match those of the master
- The control word must be operated bit by bit; do not write an integer directly
- The frequency setpoint unit is 0.01 Hz, i.e. 50.00 Hz is written as 5000
6. Summary
Core registers for Siemens G120 VFD Modbus communication:
- 40001 → Control word STW1
- 40002 → Frequency setpoint HSW
- 40003 → Status word ZSW1
- 40004 → Actual frequency HIW
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