Why does register 11028 return an illegal data address error?

Some Wattsonic Gen3 firmware versions apply a one-based offset: the register address in the protocol table must have 1 added when querying. If you receive exception code 2 on address 11028, try address 11029. Confirm against your specific firmware revision.

The gateway connects but the power register always reads zero at midday.

Verify the unit ID is set to 255. The Wattsonic LAN dongle requires exactly this ID over TCP. A mismatched unit ID causes the inverter to silently ignore requests, returning zeros or no response rather than an explicit error.

The inverter is on the network but the portal shows no data at all.

Check that port 502 is not blocked by a firewall or VLAN policy between the ModbusCloud Gateway and the inverter. Also confirm the inverter's LAN dongle has an active link LED and that the dongle is correctly configured to join your local router rather than broadcasting its own access point.

The power value appears negative or unexpectedly large. What is wrong?

Register 11028 is a signed int32 value. If the byte order returned by your inverter firmware differs from the expected big-endian format, the value will appear inverted or wildly incorrect. Confirm the ModbusCloud template data type is set to int32 and check for firmware updates that may have changed byte order behavior.

Modbus TCP

Wattsonic wattsonic (pv)

Name: Wattsonic wattsonic (pv)
Brand: Wattsonic
SKU: c4063eda-9d2f-46c5-8843-e0e8934227b2

Wattsonic

Overview

The Wattsonic hybrid inverter is a residential and light-commercial solar PV inverter with integrated battery storage management. This ModbusCloud template targets the PV meter role, reading register 11028 over Modbus TCP to deliver real-time solar generation power. Connecting via the inverter's built-in LAN dongle on port 502 with unit ID 255, the ModbusCloud Gateway polls the power register continuously. Use this template to track live PV output in your portal without additional hardware.

Use cases

Monitor real-time PV generation power to verify that string output matches expected irradiance conditions.
Track daily and seasonal PV production trends to identify panel soiling or shading degradation over time.
Alert on a drop in PV power during daylight hours to detect inverter faults or tripped DC breakers quickly.
Compare live PV output against site consumption data to calculate self-consumption ratio per billing period.

Verify PV ramp-up after grid reconnection events to confirm the Wattsonic inverter has resumed normal operation.

Installation

1Connect the Wattsonic inverter to your local network using its built-in LAN dongle, then confirm the inverter is reachable at its assigned IP address on port 502.
2Connect the ModbusCloud Gateway to the same LAN segment as the inverter, either via Ethernet or the Gateway's configured network interface.
3In the ModbusCloud portal, add a new device, import the Wattsonic (PV) template, and set the unit ID to 255 with the inverter's local IP address and port 502.
4Spot-check register 11028 in the portal's live register view to confirm a non-zero watt value is returned during daylight hours, indicating successful polling.

Things to watch for

Why does register 11028 return an illegal data address error?: Some Wattsonic Gen3 firmware versions apply a one-based offset: the register address in the protocol table must have 1 added when querying. If you receive exception code 2 on address 11028, try address 11029. Confirm against your specific firmware revision.
The gateway connects but the power register always reads zero at midday.: Verify the unit ID is set to 255. The Wattsonic LAN dongle requires exactly this ID over TCP. A mismatched unit ID causes the inverter to silently ignore requests, returning zeros or no response rather than an explicit error.
The inverter is on the network but the portal shows no data at all.: Check that port 502 is not blocked by a firewall or VLAN policy between the ModbusCloud Gateway and the inverter. Also confirm the inverter's LAN dongle has an active link LED and that the dongle is correctly configured to join your local router rather than broadcasting its own access point.
The power value appears negative or unexpectedly large. What is wrong?: Register 11028 is a signed int32 value. If the byte order returned by your inverter firmware differs from the expected big-endian format, the value will appear inverted or wildly incorrect. Confirm the ModbusCloud template data type is set to int32 and check for firmware updates that may have changed byte order behavior.

Registers (1)

1 read / 0 write

Name	Address	Function	Type	Unit	Access
power Instantaneous PV generation power, signed 32-bit integer, watts.	11028	FC03	int32	W	R

Working with Modbus in your projects?

ModbusCloud is the hardware-plus-software platform that installers use to monitor, visualise and control Modbus devices from one portal. This template is one of hundreds you can use right away.

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