Why do all _u registers show zero instead of unimplemented?

The _u registers carry the SunSpec not-implemented sentinel value for their data type, for example 0x8000 for int16 or 0xFFFF for uint16. If your portal displays zero, the template parser is not checking for sentinel values before converting raw register data. Confirm that the ModbusCloud Gateway firmware is current and the template is the latest revision.

Scale factor registers return garbage. What is wrong?

SunSpec scale factor registers (sunssf_1 through sunssf_7) are signed int16 values representing powers of ten. A raw value of 0xFFFE means -2, not 65534. If values look wrong, confirm the register type is read as int16, not uint16, and that the portal applies the exponent by multiplication rather than as a direct offset.

The gateway connects but string registers show corrupt data.

String registers span multiple Modbus addresses (the string register starts at address 100 and string_u at 116, each occupying 16 registers). Ensure the Modbus read request covers the full register block in one transaction. Partial reads split across multiple requests can produce misaligned character data.

Is it safe to write to the writable registers in this test model?

This is a test or simulator model with no live hardware, so writes carry no physical risk here. However, if you adapt write-register testing to a production SunSpec device, exercise caution: writing to registers such as ipaddr or int32_3 on real equipment may change network configuration or operational setpoints and could require a device restart or invalidate the device warranty. Always confirm the target register's effect in the manufacturer documentation before writing.

Free Modbus template: SunSpec Model 63001 — SunSpec Test Model 1

Name: SunSpec Model 63001 — SunSpec Test Model 1
Brand: SunSpec
SKU: 1dcc79c9-1269-4285-9da5-59bfd0ce4e46

SunSpec Model 63001, also called SunSpec Test Model 1, is a protocol conformance and client-validation model published by the SunSpec Alliance. It is not a physical product but a synthetic Modbus TCP register block designed to exercise every SunSpec data type in one model. The template covers all read-only and read-write points: int16, uint16, int32, uint32, acc16, acc32, acc64, int64, enum16, enum32, bitfield16, bitfield32, float32, ipaddr, multi-register strings, and seven SunSpec scale factors. Both implemented and not-implemented (sentinel) variants of each type are present. Use this template to verify that your ModbusCloud Gateway and portal correctly parse and display every SunSpec data type before commissioning a production device.

Registers (55)

55 read / 8 write

Name	Address	Function	Type	Access
id SunSpec model identifier, fixed value 63001 for this model.	0	FC03	uint16	R
l Model block length in Modbus registers.	1	FC03	uint16	R
sunssf_1 Scale factor 1, signed power-of-ten exponent applied to paired points.	2	FC03	int16	R
sunssf_2 Scale factor 2, signed power-of-ten exponent applied to paired points.	3	FC03	int16	R
sunssf_3 Scale factor 3, signed power-of-ten exponent applied to paired points.	4	FC03	int16	R
sunssf_4 Scale factor 4, signed power-of-ten exponent applied to paired points.	5	FC03	int16	R
int16_1 Signed 16-bit integer test point, read-only sample value.	6	FC03	int16	R
int16_2 Signed 16-bit integer test point, read-only sample value.	7	FC03	int16	R
int16_3 Signed 16-bit integer test point, read-only sample value.	8	FC03	int16	R
int16_4 Signed 16-bit integer test point, writable for write-path verification.	9	FC03	int16	R/W
int16_5 Signed 16-bit integer test point, read-only sample value.	10	FC03	int16	R
int16_u Signed 16-bit integer unimplemented test point, returns not-implemented sentinel.	11	FC03	int16	R
uint16_1 Unsigned 16-bit integer test point, read-only sample value.	12	FC03	uint16	R
uint16_2 Unsigned 16-bit integer test point, read-only sample value.	13	FC03	uint16	R
uint16_3 Unsigned 16-bit integer test point, read-only sample value.	14	FC03	uint16	R
uint16_4 Unsigned 16-bit integer test point, writable for write-path verification.	15	FC03	uint16	R/W
uint16_5 Unsigned 16-bit integer test point, read-only sample value.	16	FC03	uint16	R
uint16_u Unsigned 16-bit integer unimplemented test point, returns not-implemented sentinel.	17	FC03	uint16	R
acc16 16-bit accumulator test point, monotonically increasing counter value.	18	FC03	uint16	R
acc16_u 16-bit accumulator unimplemented test point, returns not-implemented sentinel.	19	FC03	uint16	R
enum16 16-bit enumeration test point, holds a coded state value.	20	FC03	uint16	R
enum16_u 16-bit enumeration unimplemented test point, returns not-implemented sentinel.	21	FC03	uint16	R
bitfield16 16-bit bitfield test point, each bit represents a boolean flag.	22	FC03	bool	R
bitfield16_u 16-bit bitfield unimplemented test point, returns not-implemented sentinel.	23	FC03	bool	R
int32_1 Signed 32-bit integer test point, read-only sample value.	24	FC03	int32	R
int32_2 Signed 32-bit integer test point, read-only sample value.	26	FC03	int32	R
int32_3 Signed 32-bit integer test point, writable for write-path verification.	28	FC03	int32	R/W
int32_4 Signed 32-bit integer test point, read-only sample value.	30	FC03	int32	R
int32_5 Signed 32-bit integer test point, read-only sample value.	32	FC03	int32	R
int32_u Signed 32-bit integer unimplemented test point, returns not-implemented sentinel.	34	FC03	int32	R
uint32_1 Unsigned 32-bit integer test point, read-only sample value.	36	FC03	uint32	R
uint32_2 Unsigned 32-bit integer test point, read-only sample value.	38	FC03	uint32	R
uint32_3 Unsigned 32-bit integer test point, writable for write-path verification.	40	FC03	uint32	R/W
uint32_4 Unsigned 32-bit integer test point, read-only; carries a constant scale factor.	42	FC03	uint32	R
uint32_5 Unsigned 32-bit integer test point, read-only sample value.	44	FC03	uint32	R
uint32_u Unsigned 32-bit integer unimplemented test point, returns not-implemented sentinel.	46	FC03	uint32	R
acc32 32-bit accumulator test point, monotonically increasing counter value.	48	FC03	uint32	R
acc32_u 32-bit accumulator unimplemented test point, returns not-implemented sentinel.	50	FC03	uint32	R
enum32 32-bit enumeration test point, holds a coded state value.	52	FC03	uint32	R
enum32_u 32-bit enumeration unimplemented test point, returns not-implemented sentinel.	54	FC03	uint32	R
bitfield32 32-bit bitfield test point, each bit represents a boolean flag.	56	FC03	uint32	R
bitfield32_u 32-bit bitfield unimplemented test point, returns not-implemented sentinel.	58	FC03	uint32	R
ipaddr IPv4 address test point, writable 32-bit encoded IP address.	60	FC03	uint32	R/W
ipaddr_u IPv4 address unimplemented test point, returns not-implemented sentinel.	62	FC03	uint32	R
int64 Signed 64-bit integer test point, writable for write-path verification.	64	FC03	int64	R/W
int64_u Signed 64-bit integer unimplemented test point, returns not-implemented sentinel.	68	FC03	int64	R
acc64 64-bit accumulator test point, monotonically increasing large counter value.	72	FC03	uint64	R
acc64_u 64-bit accumulator unimplemented test point, returns not-implemented sentinel.	76	FC03	uint64	R
float32 IEEE 754 32-bit float test point, writable for write-path verification.	96	FC03	float32	R/W
float32_u IEEE 754 32-bit float unimplemented test point, returns not-implemented sentinel.	98	FC03	float32	R
string Multi-register string test point, writable ASCII character array.	100	FC03	string	R/W
string_u Multi-register string unimplemented test point, returns not-implemented sentinel.	116	FC03	string	R
sunssf_5 Scale factor 5, signed power-of-ten exponent applied to paired points.	132	FC03	int16	R
sunssf_6 Scale factor 6, signed power-of-ten exponent applied to paired points.	133	FC03	int16	R
sunssf_7 Scale factor 7, signed power-of-ten exponent applied to paired points.	134	FC03	int16	R