All register values read as zero or max. What is wrong?

The EM100 uses big-endian (MSB-first) byte order within each 16-bit word, and 32-bit values span two consecutive registers with the high word first. If your gateway byte-swap or word-swap settings do not match this, every int32 register will decode incorrectly. Verify the word order setting in the ModbusCloud Gateway RTU configuration.

The gateway connects but no readings appear in the portal.

Confirm that the Modbus RTU slave address on the EM100 matches the unit ID entered in the portal. Also check that baud rate and parity on the meter (typically 9600 baud, even parity) match the Gateway serial port settings. A mismatch on either will produce silence with no CRC errors.

Values are noisy or the meter drops off the bus intermittently.

RS485 buses require proper termination. Place a 120-ohm resistor between the A and B lines at the far end of the bus, and connect the cable shield to ground at the master side only. On the EM100 specifically, connect terminal A- to terminal T on the last device on the bus to activate the built-in termination.

Function code 4 returns an exception but function code 3 works. Is that normal?

Yes, this is expected behaviour. The EM100 register map is addressed via function code 04 (Read Input Registers), but according to the Carlo Gavazzi communication protocol, functions 03h and 04h have exactly the same effect and can be used interchangeably. The template uses FC4, which is the primary mapping. Switching to FC3 at the same physical addresses also works.

Free Modbus template: CarloGavazzi EM100

The CarloGavazzi EM100 is a single-phase energy analyser designed for DIN-rail mounting in residential, commercial, and light-industrial metering applications. It communicates over RS485 using Modbus RTU and exposes six key electrical measurements: voltage, current, active power, apparent power, reactive power, and grid frequency. This ModbusCloud template maps those registers directly, giving your portal a complete real-time picture of single-phase load behaviour with no manual configuration required. Use it in any installation where a compact, read-only power quality snapshot is needed alongside other RS485 devices on a shared bus.

Name	Address	Function	Type	Unit	Access
voltage Line voltage at the meter input, in volts.	0	FC04	int32	V	R
current Line current drawn by the measured load, in amperes.	2	FC04	int32	A	R
active_power Instantaneous active power, positive for import, in watts.	4	FC04	int32	W	R
apparent_power Instantaneous apparent power (volt-amperes).	6	FC04	int32	VA	R
reactive_power Instantaneous reactive power, in volt-amperes reactive.	8	FC04	int32	var	R
frequency AC supply frequency, typically 50 or 60 Hz.	15	FC04	uint16	Hz	R