Plexlog Plexlog (pv)

Installation

1. 1Enable Modbus TCP on the Plexlog data-logger by opening the device's web interface, navigating to the communication or Modbus section, and confirming the Modbus TCP server is active on port 502 (or 503 depending on your firmware version).
2. 2Connect the Plexlog data-logger to the same LAN as the ModbusCloud Gateway, ensuring both devices share IP reachability and that no firewall blocks the configured Modbus TCP port.
3. 3In the ModbusCloud portal, add your Gateway, then import the Plexlog (pv) template and assign unit ID 1 (default); enter the data-logger's IP address and the port confirmed in step 1.
4. 4Perform a live read of the power register (address 0, FC4, int32) in the portal's register inspector and verify the value matches the current PV output shown on the Plexlog web interface.

Things to watch for

01

Why does the gateway return an 'illegal function' error for the power register?

The Plexlog data-logger exposes the PV power register via function code 4 (Read Input Registers). Using function code 3 (Read Holding Registers) against the same address causes exception code 1. Confirm the template is using FC4 and that your Modbus TCP port matches the one enabled in the logger's communication settings.

02

The gateway connects but the power value reads zero or null. What now?

First check that the Modbus TCP server is enabled on the Plexlog device, not just the API. Then confirm the unit ID is set to 1. If it still reads zero, verify that at least one inverter is actively reporting to the logger; the logger will not forward data from inverters it has lost contact with.

03

Which TCP port does the Plexlog data-logger use for Modbus?

Plexlog documents both port 502 (standard Modbus TCP) and port 503 depending on logger model and firmware configuration. Check the communication settings in the Plexlog web interface and ensure the same port is entered in the ModbusCloud portal. Mismatched ports cause silent connection failures.

04

The power register returns an unexpectedly large or negative value. What could cause this?

The register is typed as int32 and spans two consecutive 16-bit Modbus words. If the client reads only one word or reverses word order, the decoded value will be incorrect. Confirm the template is decoding both words as a big-endian int32, and check that no scaling factor has been applied accidentally in the portal configuration.

Registers (1)

1 read / 0 write

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