The mn and md registers return empty or garbled strings. Why?

SunSpec string registers are null-padded and encoded in big-endian byte order. If your client swaps byte order or trims null bytes incorrectly, strings appear corrupted. Ensure the ModbusCloud Gateway reads the full register width without byte-swapping: mn spans 16 registers and md spans 16 registers from their respective offsets.

Polling returns a Modbus exception on register 0. What is wrong?

Some devices place the SunSpec map at base address 40000 or 50000, not at offset 0. The register addresses in this template are relative offsets within the SunSpec block. Confirm the device base address in its documentation and configure the ModbusCloud Gateway base offset accordingly so address 0 resolves to the correct absolute register.

No values appear even though the gateway shows a TCP connection.

Check the unit ID. Many SunSpec devices default to unit ID 1, but multi-inverter gateways use higher IDs (for example, 125 for the gateway itself and 126 and above for attached inverters). Assign the correct unit ID in the ModbusCloud portal and re-poll.

Is it safe to write to the da register to change the unit ID remotely?

Writing to da changes the device Modbus unit ID immediately and will break all existing polling sessions targeting the old ID. Before writing, document the current value from the id and sn registers to confirm you are addressing the correct device. On some devices, writing an already-in-use unit ID on the bus causes address conflicts and communication failures for all devices on that segment.

Free Modbus template: SunSpec Model 1 — Common

SunSpec Model 1, the Common Block, is the mandatory identification header present on every SunSpec-compliant device across inverters, energy meters, battery systems, and HVAC controllers. Over Modbus TCP, this template reads the model identifier, block length, manufacturer name, device model, options label, firmware version, and serial number, and exposes the device address register for read and write access. Importing this template into your ModbusCloud portal gives you a verified device fingerprint, making it straightforward to confirm which physical unit is connected at any unit ID before querying its functional models.

Name	Address	Function	Type	Access
id SunSpec model identifier, value 1 for the Common Block.	0	FC03	uint16	R
l Number of Modbus registers in this model block, excluding id and l.	1	FC03	uint16	R
mn Manufacturer name string, registered with SunSpec for compliance.	2	FC03	string	R
md Device model name string, manufacturer-specific, up to 32 characters.	18	FC03	string	R
opt Options string, manufacturer-specific device option or configuration label.	34	FC03	string	R
vr Firmware version string, manufacturer-specific, up to 16 characters.	42	FC03	string	R
sn Device serial number string, mandatory for SunSpec compliance.	50	FC03	string	R
da Modbus unit ID of this device, readable and writable for addressing.	66	FC03	uint16	R/W