使用pymodbus读取SMA STP6.0逆变器温度遇AttributeError问题求助

That error means your SMA inverter is sending back a Modbus error response instead of the expected register data. Let's break down how to diagnose and fix this step by step:

1. First, Identify the Exact Modbus Error #

The first thing to do is see what specific error code the inverter is returning. Modify your get_device_block method to check for the error and print details:

from pymodbus.exceptions import ExceptionResponse

def get_device_block(self, offset, length):
    response = self.client.read_holding_registers(offset, length, slave=self.slave_id)
    # Add this check to reveal the error
    if isinstance(response, ExceptionResponse):
        print(f"Modbus Error Received: Code {hex(response.exception_code)}")
        print(f"Error Description: {response}")
        return None
    return SunspecDecoder.fromRegisters(response.registers)

Common error codes you might encounter:

• 0x02 (Illegal Data Address): The register range you're requesting doesn't exist on your inverter.
• 0x03 (Illegal Data Value): The request format/length is invalid.
• 0x01 (Illegal Function): Unlikely here, but would mean using the wrong Modbus function code.

2. Verify SMA Inverter Modbus TCP Settings #

SMA inverters don't have Modbus TCP enabled by default. You need to turn it on manually:

• Access the inverter's web interface using the IP 192.168.178.110.
• Navigate to Settings > Communication > Modbus TCP.
• Enable Modbus TCP, confirm the port is set to 502 (default), and note the Slave ID (usually 1, but double-check).
• Save changes and reboot the inverter if prompted.

3. Confirm the Sunspec Starting Register #

SMA's Sunspec implementation typically starts at Modbus register 40001 (1-based), which translates to 40000 in 0-based indexing (the format PyModbus uses). However, some STP6.0 models might use a different offset. If you get an Illegal Data Address error, cross-reference SMA's official documentation for your exact inverter model to confirm the correct starting register for Sunspec.

4. Check Network Connectivity #

• Ensure your Ubuntu machine can ping the inverter at 192.168.178.110.
• Verify no firewall (on your machine or network) is blocking port 502.
• Test port accessibility with telnet 192.168.178.110 502—if it connects, the port is open.

5. Adjust the Slave ID in Your Client #

If your inverter's Slave ID isn't 1 (the default in many examples), update your client initialization to use the correct ID:

def create_sunspec_sync_client(host):
    client = ModbusTcpClient(host, port=502)
    # Replace YOUR_SLAVE_ID with the value from your inverter's settings
    sunspec_client = SunspecClient(client, slave_id=YOUR_SLAVE_ID)
    sunspec_client.initialize()
    return sunspec_client

6. Update PyModbus to the Latest Stable Version #

Older versions of PyModbus might have compatibility issues with SMA's Sunspec implementation. Upgrade using:

pip3 install --upgrade pymodbus

Once you've identified the specific error code, you can narrow down the issue further. For example, an Illegal Data Address points to an incorrect register offset or disabled Modbus feature, while a connection error would indicate network/firewall problems.

内容的提问来源于stack exchange，提问作者Alfred Elkerbout