Crowcon Nimbus gas controller

Register map(s) for this device, each at the trust rung it earned. Addresses are 0-based as on the wire. Word order and scaling are confirmed at the hardware-verified rung and at no rung below it.

interop-verified

Read + decoded cleanly over a real network vs an independent third-party Modbus test server (transport and framing; reads are remapped into the server's register window, so the map's own addresses are NOT exercised). Does NOT prove word order/scaling against the actual device.

point	address (0-based)	type	scale	unit
gas_level	99	I16	0.1	% FSD
mode	100	I16	1	enum
status	101	I16	1	enum
detector_signal_rate_of_change	102	I16	0.01
inst_gas_reading	103	I16	0.1
obscuration_factor	104	I16	0.1	%
supply_voltage	105	I16	0.01	V
temperature	106	I16	0.1	oC
gas_det_level_at_zero	303	I16	1	raw
ref_det_level_at_zero	304	I16	1
temp_at_zero	305	I16	0.1	oC
gas_det_zero_drift	306	I16	1
ref_det_zero_drift	307	I16	1
temp_at_auto_zero	308	I16	0.1
gas_det_signal_gain_at_fsd	309	I16	1
ref_det_signal_gain_at_fsd	310	I16	1
temp_at_fsd	311	I16	0.1
level_2_alarm_threshold	499	I16	0.1	% FSD
level_1_alarm_threshold	500	I16	0.1	% FSD
level_1_falling_alarm_threshold	501	I16	0.1
level_2_falling_alarm_threshold	502	I16	0.1
alarm_threshold_hysteresis	503	I16	0.1
lamp_sense	575	I16	0.1
supply_voltage_test	576	I16	0.01
reg_supply_sense	577	I16	0.001
temperature_test	578	I16	0.1

link settings as documented (unverified): RTU; default 9600 8N2; unit ID 1; FC 03,16; RS485 half-duplex multi-drop asynchronous serial communications link.

bench facts as documented (unverified)

A/B polarity	differential of between 2 and 6 volts
isolation	conforming to the RS458 standard (-7 to +12 volts)
wiring notes	2 wire, half duplex, multi-drop
max registers/read	125
response timeout	500 ms
inter-frame delay	10 ms
broadcast	supported
protocol notes	Global address 000 is used for broadcast requests, which are validated and actioned but not responded to.
model register	0
serial register	4
firmware register	1
FC 43 device ID	not supported
power	supply set to 24 volts
doc revision	Issue No: 3, Date: 09-Mar-06

⚠ disputed: gas_level @ 99 — disputed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012) which lists Gas Level at register 100

⚠ disputed: mode @ 100 — disputed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012) which lists Mode at register 101

⚠ disputed: status @ 101 — disputed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012) which lists Status at register 102

⚠ disputed: detector_signal_rate_of_change @ 102 — disputed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012) which lists Detector Signal Rate of Change at register 103

⚠ disputed: inst_gas_reading @ 103 — disputed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012) which lists Inst Gas Reading at register 104

⚠ disputed: obscuration_factor @ 104 — disputed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012) which lists Obscuration Factor at register 105

⚠ disputed: gas_det_level_at_zero @ 303 — disputed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012) which lists Gas Det Level at Zero at register 304

⚠ disputed: ref_det_level_at_zero @ 304 — disputed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012) which lists Ref Det Level at Zero at register 305

field reports — community-sourced, unverified (checked 2026-06-11)

The register map summary provided contains off-by-one errors across multiple registers compared to the official NIM-012 specification. For example, Gas Level is at register 100 (not 99), Mode is at 101 (not 100), Status is at 102 (not 101), and Lamp Sense is at 576 (not 575). [source]
confirmed: Document revision 'Issue No: 3, Date: 09-Mar-06' — confirmed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012)
confirmed: Register addresses mode @ 101, status @ 102, detector_signal_rate_of_change @ 103, inst_gas_reading @ 104, obscuration_factor @ 105 — confirmed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012)
confirmed: Register addresses gas_det_level_at_zero @ 304, ref_det_level_at_zero @ 305 — confirmed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012)
confirmed: Register addresses level_2_alarm_threshold @ 500, level_1_alarm_threshold @ 501, level_1_falling_alarm_threshold @ 502 — confirmed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012)
confirmed: Register addresses lamp_sense @ 576, supply_voltage_test @ 577, reg_supply_sense @ 578 — confirmed by Crowcon Nimbus ModBus Interface Specification (Doc No: NIM-012)

The trust ladder

Each rung states what it proved and what it did not. Gray until proven; green is earned by hardware only.

generated — A prompt produced it. Unproven — anyone can regenerate this.
structure-verified — Decode path is structurally sound (addresses, widths, finite values). Does NOT prove word order or scaling.
interop-verified — Read + decoded cleanly over a real network vs an independent third-party Modbus test server (transport and framing; reads are remapped into the server's register window, so the map's own addresses are NOT exercised). Does NOT prove word order/scaling against the actual device.
simulator-verified — Decoded correctly against a protocol emulator seeded with known-true values — catches word-order/scaling errors vs the emulator, not the physical device.
hardware-verified x1 — Matched a real device with operator-attested readings as ground truth — the only rung that confirms word order + scaling on the wire.

If your device isn't here, upload its register map. Generation is free, and the connector keeps the rung it earns under testing.

To prove a connector against your own device, order hardware verification. If it doesn't verify, you don't pay.

Platform builders can license the verified library: machine-readable maps, the firmware matrix, API access.