Crowcon Gasmaster III gas panel

Register map(s) for this device, with a note of how far each has been checked. Addresses are 0-based, as on the wire. Scale and byte order are confirmed only at the hardware-verified rung.

structure-verified

Decode path is structurally sound (addresses, widths, finite values). Does NOT prove word order or scaling.

point	address (0-based)	type	scale	unit
Instrument identification	1	U16	1
Manufacturer	2	U16	1
Software version	3	U16	1
Instrument serial number	4	U16	1
System Name	5	U16	1
Modbus Address	50	U16	1
Modbus Stop bit Config	51	U16	1
Next Service Due	52	I32BE	1	s
Language	53	U16	1
System Type	54	U16	1
Menu Display Contrast	55	U16	1
Channel Display Contrast	56	U16	1
Common Relay Low Type	57	U16	1
Common Relay Low Energisation	58	U16	1
Common Relay High Type	59	U16	1
Common Relay High Energisation	60	U16	1
Common Relay Fault Type	61	U16	1
Common Relay Fault Energisation	62	U16	1
Sounder AV Drive type	63	U16	1
Beacon AV Drive type	64	U16	1
Supervisor Password	65	U16	1
System Clock Adjustment	66	I32BE	1
Mains Fail Config	67	U16	1
Pellistor Saver Threshold	68	F32BE	1	%LEL
Ch1.Location	100	U16	1
Ch1.GasName	101	U16	1
Ch1.Type	102	U16	1
Ch1.Range	103	F32BE	1
Ch1.Units	104	U16	1
Ch1.Alarm Low Level	105	F32BE	1
Ch1.Alarm Low Hysteresis	106	F32BE	1
Ch1.Alarm Low Sense	107	U16	1
Ch1.Relay Low Type	108	U16	1
Ch1.Relay Low Energisation	109	U16	1
Ch1.Alarm High Level	110	F32BE	1
Ch1.Alarm High Sense	111	U16	1
Ch1.Relay High Type	112	U16	1
Ch1.Relay High Energisation	113	U16	1
Ch1.Interpret Low	114	U16	1
Ch1.Apply ZFS	115	U16	1
Ch1.Fire Reset Time	116	U16	1	s
Ch1.Stabilisation Time	117	U16	1	s
Ch1.Alarm 1 Silent	118	U16	1
Ch1.Input zero	119	F32BE	1
Ch1.Input scale	120	F32BE	1
Ch1.Output zero	121	F32BE	1
Ch1.Output scale	122	F32BE	1
Ch1.Input Scale Limit	123	F32BE	1
Ch2.Location	200	U16	1
Ch2.GasName	201	U16	1
Ch2.Type	202	U16	1
Ch2.Range	203	F32BE	1
Ch2.Units	204	U16	1
Ch2.Alarm Low Level	205	F32BE	1
Ch2.Alarm Low Hysteresis	206	F32BE	1
Ch2.Alarm Low Sense	207	U16	1
Ch2.Relay Low Type	208	U16	1
Ch2.Relay Low Energisation	209	U16	1
Ch2.Alarm High Level	210	F32BE	1
Ch2.Alarm High Sense	211	U16	1
Ch2.Relay High Type	212	U16	1
Ch2.Relay High Energisation	213	U16	1
Ch2.Interpret Low	214	U16	1
Ch2.Apply ZFS	215	U16	1
Ch2.Fire Reset Time	216	U16	1	s
Ch2.Stabilisation Time	217	U16	1	s
Ch2.Alarm 1 Silent	218	U16	1
Ch2.Input zero	219	F32BE	1
Ch2.Input scale	220	F32BE	1
Ch2.Output zero	221	F32BE	1
Ch2.Output scale	222	F32BE	1
Ch2.Input Scale Limit	223	F32BE	1
Ch3.Location	300	U16	1
Ch3.GasName	301	U16	1
Ch3.Type	302	U16	1
Ch3.Range	303	F32BE	1
Ch3.Units	304	U16	1
Ch3.Alarm Low Level	305	F32BE	1
Ch3.Alarm Low Hysteresis	306	F32BE	1
Ch3.Alarm Low Sense	307	U16	1
Ch3.Relay Low Type	308	U16	1
Ch3.Relay Low Energisation	309	U16	1
Ch3.Alarm High Level	310	F32BE	1
Ch3.Alarm High Sense	311	U16	1
Ch3.Relay High Type	312	U16	1
Ch3.Relay High Energisation	313	U16	1
Ch3.Interpret Low	314	U16	1
Ch3.Apply ZFS	315	U16	1
Ch3.Fire Reset Time	316	U16	1	s
Ch3.Stabilisation Time	317	U16	1	s
Ch3.Alarm 1 Silent	318	U16	1
Ch3.Input zero	319	F32BE	1
Ch3.Input scale	320	F32BE	1
Ch3.Output zero	321	F32BE	1
Ch3.Output scale	322	F32BE	1
Ch3.Input Scale Limit	323	F32BE	1
Ch4.Location	400	U16	1
Ch4.GasName	401	U16	1
Ch4.Type	402	U16	1
Ch4.Range	403	F32BE	1
Ch4.Units	404	U16	1
Ch4.Alarm Low Level	405	F32BE	1
Ch4.Alarm Low Hysteresis	406	F32BE	1
Ch4.Alarm Low Sense	407	U16	1
Ch4.Relay Low Type	408	U16	1
Ch4.Relay Low Energisation	409	U16	1
Ch4.Alarm High Level	410	F32BE	1
Ch4.Alarm High Sense	411	U16	1
Ch4.Relay High Type	412	U16	1
Ch4.Relay High Energisation	413	U16	1
Ch4.Interpret Low	414	U16	1
Ch4.Apply ZFS	415	U16	1
Ch4.Fire Reset Time	416	U16	1	s
Ch4.Stabilisation Time	417	U16	1	s
Ch4.Alarm 1 Silent	418	U16	1
Ch4.Input zero	419	F32BE	1
Ch4.Input scale	420	F32BE	1
Ch4.Output zero	421	F32BE	1
Ch4.Output scale	422	F32BE	1
Ch4.Input Scale Limit	423	F32BE	1
Time	500	U32BE	1	s
Status	501	U16	1
System Fault 1	502	U32BE	1
System Fault 2	503	U32BE	1
System Warning 1	504	U32BE	1
System Warning 2	505	U32BE	1
Channel 1 Level	506	F32BE	1
Channel 1 Status	507	U16	1
Channel 2 Level	508	F32BE	1
Channel 2 Status	509	U16	1
Channel 3 Level	510	F32BE	1
Channel 3 Status	511	U16	1
Channel 4 Level	512	F32BE	1
Channel 4 Status	513	U16	1
Channel 1 Inhibit	540	U16	1
Channel 1 Action Zero	541	U16	1
Channel 1 Cal Level	542	F32BE	1
Channel 1 Cal Action	543	U16	1
Channel 1 OP Cal Control	544	U16	1
Channel 1 OP Cal Level	545	F32BE	1
Channel 1 Pellistor saver disabled	546	U16	1
Channel 2 Inhibit	550	U16	1
Channel 2 Action Zero	551	U16	1
Channel 2 Cal Level	552	F32BE	1
Channel 2 Cal Action	553	U16	1
Channel 2 OP Cal Control	554	U16	1
Channel 2 OP Cal Level	555	F32BE	1
Channel 2 Pellistor saver disabled	556	U16	1
Channel 3 Inhibit	560	U16	1
Channel 3 Action Zero	561	U16	1
Channel 3 Cal Level	562	F32BE	1
Channel 3 Cal Action	563	U16	1
Channel 3 OP Cal Control	564	U16	1
Channel 3 OP Cal Level	565	F32BE	1
Channel 3 Pellistor saver disabled	566	U16	1
Channel 4 Inhibit	570	U16	1
Channel 4 Action Zero	571	U16	1
Channel 4 Cal Level	572	F32BE	1
Channel 4 Cal Action	573	U16	1
Channel 4 OP Cal Control	574	U16	1
Channel 4 OP Cal Level	575	F32BE	1
Channel 4 Pellistor saver disabled	576	U16	1
Accept Reset	600	U16	1
NVM control	601	U16	1
Protection	602	U16	1
Power Up Test	603	U16	1
Relay Stimulation Sequence	604	U16	1
Relay Monitor	605	U16	1
Analogue Out1 Stimulation	606	U16	1
Analogue Out2 Stimulation	607	U16	1
Analogue Out3 Stimulation	608	U16	1
Analogue Out4 Stimulation	609	U16	1
DAC0 Output	610	U16	1
DAC1 Output	611	U16	1
Indicator Stimulation	612	U16	1
Chan LCD Test	613	U16	1
Chan LCD Seq	614	U16	1
Menu LCD Test	615	U16	1
Menu LCD Seq	616	U16	1
LCD Backlight	617	U16	1
MUX control – Ch1	618	U16	1
MUX control – Ch2	619	U16	1
MUX control – Ch3	620	U16	1
MUX control – Ch4	621	U16	1
Raw ADC – Ch1	622	U16	1
Raw ADC – Ch2	623	U16	1
Raw ADC – Ch3	624	U16	1
Raw ADC – Ch4	625	U16	1
Raw ADC – PSU	626	U16	1
Raw ADC – Vsys	627	U16	1
Raw ADC – P12V	628	U16	1
Raw ADC – Check Low	629	U16	1
Raw ADC – Check High	630	U16	1
Raw ADC – VLCD0	631	U16	1
Raw ADC – VLCD1	632	U16	1
Button	633	U16	1
Fire Reset	634	U16	1
Battery Switch	635	U16	1
Read control	700	U16	1
Service event time and date	701	U32BE	1	s
Event 1 time	702	U32BE	1
Event 1 IDs	703	U16	1
Event 1 data word	704	U32BE	1
Event 2 time	705	U32BE	1
Event 2 IDs	706	U16	1
Event 2 data word	707	U32BE	1
Event 3 time	708	U32BE	1
Event 3 IDs	709	U16	1
Event 3 data word	710	U32BE	1
Event 4 time	711	U32BE	1
Event 4 IDs	712	U16	1
Event 4 data word	713	U32BE	1
Event 5 time	714	U32BE	1
Event 5 IDs	715	U16	1
Event 5 data word	716	U32BE	1
Event 6 time	717	U32BE	1
Event 6 IDs	718	U16	1
Event 6 data word	719	U32BE	1
Event 7 time	720	U32BE	1
Event 7 Ids	721	U16	1
Event 7 data word	722	U32BE	1
Event 8 time	723	U32BE	1
Event 8 Ids	724	U16	1
Event 8 data word	725	U32BE	1
Event 9 time	726	U32BE	1
Event 9 Ids	727	U16	1
Event 9 data word	728	U32BE	1
Event 10 time	729	U32BE	1
Event 10 Ids	730	U16	1
Event 10 data word	731	U32BE	1
Text string ident	800	U16	1
Text string length (L)	801	U16	1
Primary language text	802	U16	1
Configurable language text	803	U16	1

link settings as documented (unverified): RTU; default 9600 8N1; unit ID 1; FC 03,16; A silent interval of 5.7mS is used to define the termination of a data packet. On receipt of a message requiring a response, the instrument will pause for a guaranteed period of at least 50mS before transmission will commence.

bench facts as documented (unverified)

inter-frame delay	5 ms
broadcast	supported
protocol notes	On receipt of a message requiring a response, the instrument will pause for a guaranteed period of at least 50mS before transmission will commence.
model register	1
serial register	4
firmware register	3
identification notes	Manufacturer is at address 2.
FC 43 device ID	not supported
doc revision	FGM3-002 Issue 2 January 2015

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

confirmed: Document revision FGM3-002 Issue 2 January 2015 — confirmed by Crowcon Gasmaster Modbus Instructions document [1.1.1]
confirmed: Baud rate 9600, RTU framing, and 1 stop bit (configurable) — confirmed by Crowcon Gasmaster Modbus Instructions Section 2.1
confirmed: Silent interval of 5.7mS and response pause of at least 50mS — confirmed by Crowcon Gasmaster Modbus Instructions Section 2.2
confirmed: Instrument identification registers (Model @ 1, Manufacturer @ 2, Software version @ 3, Serial @ 4) — confirmed by Crowcon Gasmaster Modbus Instructions Section 3.1
confirmed: Runtime registers (Time @ 500, Status @ 501, System Fault 1 @ 502, System Fault 2 @ 503) — confirmed by Crowcon Gasmaster Modbus Instructions Section 3.4
confirmed: Raw ADC registers (Raw ADC Ch1 @ 622 through Raw ADC VLCD1 @ 632) — confirmed by Crowcon Gasmaster Modbus Instructions Section 3.4

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.
coherence-checked — Round-trips through a real Modbus stack with no overlapping addresses and a word-order-sensitive codec — the map is internally coherent and wire-decodable. Does NOT prove byte-order or scaling match a real device: the emulator is seeded from the map's own types, so a uniformly wrong byte-order still round-trips. Only hardware-verified confirms byte-order/scale on the wire.
hardware-verified (software-key) x1 — Matched a real device with operator-attested readings as ground truth — the only rung that confirms word order + scaling on the wire.

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