All sensor readings show zero or 0x7FFF. What is wrong?

The GreenString reports 0x7FFF (32767) as the SunSpec not-implemented sentinel for int16 points when a sensor is absent or not connected. Check that each physical sensor is wired to its designated input on the probe or auxiliary card. Unconnected channels will always return this sentinel.

Voltage and current values look wrong by a factor of ten or one hundred. Why?

The raw register values for sensor1voltage through sensor7voltage and sensor1current through sensor7current must be multiplied by 10 raised to the power of sensorv_sf or sensora_sf respectively. If your Modbus client does not apply these SunSpec scale factors automatically, the displayed values will be off by an order of magnitude. Read the scale factor registers first and apply them in your client.

The gateway connects but no data arrives from the GreenString card.

Verify the RS485 bus has exactly one 120-ohm termination resistor at each physical end of the cable run. A missing or doubled termination causes signal reflections that corrupt frames. Also confirm the unit ID on the card matches the ID configured in the portal, and that baud rate and parity settings agree on both ends.

The resetaccumulators or reset registers are in the template. Is it safe to write to them?

Both registers act as control commands: writing to resetaccumulators clears stored energy or diagnostic counters, and writing to reset triggers a soft device restart, which will interrupt data collection momentarily. Do not issue these commands during active monitoring sessions or from automated rules without a deliberate operator action, as unintended resets can corrupt accumulated data and may affect connected protection relay state.

Free Modbus template: SunSpec Model 64020 — Mersen GreenString

Name: SunSpec Model 64020 — Mersen GreenString
Brand: SunSpec
SKU: e6ad46ae-23e0-47f2-bb1c-5f051c4f28cd

The Mersen GreenString is a string-level monitoring card system for mid- and large-scale photovoltaic combiner boxes. Using Modbus RTU over isolated RS485, this SunSpec Model 64020 template reads per-string DC voltage and current across up to seven channels, a frequency sensor, up to five auxiliary and one probe temperature inputs, and a main board temperature. It also exposes three relay status registers. Connecting the GreenString to ModbusCloud lets O&M teams detect string underperformance, thermal anomalies, and relay events without visiting the site.

Registers (32)

32 read / 0 write

Name	Address	Function	Type	Unit	Access
id SunSpec model identifier, fixed value 64020 for GreenString.	0	FC03	uint16		R
l Model block length in 16-bit registers.	1	FC03	uint16		R
aux0tmp Auxiliary temperature sensor 0 reading, degrees Celsius.	2	FC03	int16	°C	R
aux1tmp Auxiliary temperature sensor 1 reading, degrees Celsius.	3	FC03	int16	°C	R
aux2tmp Auxiliary temperature sensor 2 reading, degrees Celsius.	4	FC03	int16	°C	R
aux3tmp Auxiliary temperature sensor 3 reading, degrees Celsius.	5	FC03	int16	°C	R
aux4tmp Auxiliary temperature sensor 4 reading, degrees Celsius.	6	FC03	int16	°C	R
probetmp Probe card temperature sensor reading, degrees Celsius.	7	FC03	int16	°C	R
maintmp Main board temperature reading, degrees Celsius.	8	FC03	int16	°C	R
sensorv_sf Scale factor exponent applied to all voltage sensor readings.	9	FC03	int16		R
sensora_sf Scale factor exponent applied to all current sensor readings.	10	FC03	int16		R
sensorhz_sf Scale factor exponent applied to the frequency sensor reading.	11	FC03	int16		R
sensor1voltage String 1 DC voltage, scaled by sensorv_sf, volts.	12	FC03	int16	V	R
sensor2voltage String 2 DC voltage, scaled by sensorv_sf, volts.	13	FC03	int16	V	R
sensor3voltage String 3 DC voltage, scaled by sensorv_sf, volts.	14	FC03	int16	V	R
sensor4voltage String 4 DC voltage, scaled by sensorv_sf, volts.	15	FC03	int16	V	R
sensor5voltage String 5 DC voltage, scaled by sensorv_sf, volts.	16	FC03	int16	V	R
sensor6voltage String 6 DC voltage, scaled by sensorv_sf, volts.	17	FC03	int16	V	R
sensor7voltage String 7 DC voltage, scaled by sensorv_sf, volts.	18	FC03	int16	V	R
sensor1current String 1 DC current, scaled by sensora_sf, amperes.	19	FC03	int16	A	R
sensor2current String 2 DC current, scaled by sensora_sf, amperes.	20	FC03	int16	A	R
sensor3current String 3 DC current, scaled by sensora_sf, amperes.	21	FC03	int16	A	R
sensor4current String 4 DC current, scaled by sensora_sf, amperes.	22	FC03	int16	A	R
sensor5current String 5 DC current, scaled by sensora_sf, amperes.	23	FC03	int16	A	R
sensor6current String 6 DC current, scaled by sensora_sf, amperes.	24	FC03	int16	A	R
sensor7current String 7 DC current, scaled by sensora_sf, amperes.	25	FC03	int16	A	R
sensor8 Frequency sensor reading, scaled by sensorhz_sf, hertz.	26	FC03	uint16	Hz	R
relay1 Status word for external relay output 1.	27	FC03	uint16		R
relay2 Status word for external relay output 2.	28	FC03	uint16		R
relay3 Status word for external relay output 3.	29	FC03	uint16		R
resetaccumulators Accumulator reset control register; write to clear stored counters.	30	FC03	uint16		R
reset Device reset control register; write to trigger a soft reset.	31	FC03	uint16		R