Eurotherm 2404/2408 controller (needs comms module)

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.

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.

point	address (0-based)	type	scale
process_variable	1	I16	1
target_setpoint	2	I16	1
output_level	3	I16	1
working_setpoint	5	I16	1
valve_position	53	I16	1
heater_current	80	I16	1
alarm_1_setpoint	13	I16	1
alarm_2_setpoint	14	I16	1
alarm_3_setpoint	81	I16	1
alarm_4_setpoint	82	I16	1
auto_manual_select	273	U16	1
fast_status_byte	74	U16	1
summary_output_status_word	75	U16	1
control_status_word	76	U16	1
instrument_status_word	77	U16	1
digital_input_status_word	87	U16	1
input_1_measured_value	202	I16	1
input_2_measured_value	208	I16	1
input_1_cold_junction_temp	215	I16	1
input_2_cold_junction_temp	216	I16	1
process_variable_float	32770	F32BE	1
target_setpoint_float	32772	F32BE	1
output_level_float	32774	F32BE	1
working_setpoint_float	32778	F32BE	1
valve_position_float	32874	F32BE	1
heater_current_float	32928	F32BE	1

link settings as documented (unverified): RTU; baud 1200/2400/4800/9600/19200; FC 03,04,16

⚠ Broadcast is only recommended for systems where failure to communicate a value due to physical failure of wiring or other equipment will not cause damage to equipment. — Starkest reads only; we never write a control register.

bench facts as documented (unverified)

terminals	HF, HE, HD for RS232/RS485; F1-F5/HE, HF, HB, HC, HD for RS422
A/B polarity	RX+, RX-, TX+, TX- for RS422; HF (B/B+), HE (A/A+) for RS485
termination	220 ohm termination resistor on Rx terminals of last controller in chain
isolation	fully isolated communications circuitry
shield/ground	copper braid shield connected to a noise free ground
broadcast	supported
protocol notes	For 2400 firmware versions 3.00 and greater, a facility allows block writes to continue even if values in the block are not currently writeable by writing 1 to register 220.
model register	12544
doc revision	Part No HA026230 Issue 2.0 Feb-00
firmware applicability	2400 firmware versions 3.00 and greater

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

Data Register Skew Problem: When communicating with multiple Eurotherm 2404 controllers via a Moxa MGate MB3480 gateway to Ignition, registers are offset/skewed by one place per increasing Modbus address (e.g., address 9 is offset by 1 compared to address 8). [source]
RS-485 Signal Polarity Reversal: Eurotherm controllers use a non-standard labeling convention where terminal assignments (HE and HF) can result in reversed polarity when connected directly to some Modbus RTU masters (such as Mitsubishi GOT HMIs) using documented pinouts, requiring swapping the RS-485 differential pairs. [source]
confirmed: Part No HA026230 Issue 2.0 Feb-00 — confirmed by Eurotherm 2000 Series Communications Handbook [1.1.3]
confirmed: For 2400 firmware versions 3.00 and greater, a facility allows block writes to continue even if values in the block are not currently writeable by writing 1 to register 220 — confirmed by Eurotherm 2000 Series Communications Handbook
confirmed: process_variable @ 1, target_setpoint @ 2, output_level @ 3, working_setpoint @ 5, valve_position @ 53, heater_current @ 80 — confirmed by Eurotherm 2000 Series Communications Handbook
confirmed: alarm_1_setpoint @ 13, alarm_2_setpoint @ 14, alarm_3_setpoint @ 81, alarm_4_setpoint @ 82 — confirmed by Eurotherm 2000 Series Communications Handbook
confirmed: fast_status_byte @ 74, summary_output_status_word @ 75, control_status_word @ 76, instrument_status_word @ 77, digital_input_status_word @ 87 — confirmed by Eurotherm 2000 Series Communications Handbook
confirmed: input_1_measured_value @ 202, input_2_measured_value @ 208, input_1_cold_junction_temp @ 215, input_2_cold_junction_temp @ 216 — confirmed by Eurotherm 2000 Series Communications Handbook
confirmed: process_variable_float @ 32770, target_setpoint_float @ 32772, output_level_float @ 32774, working_setpoint_float @ 32778, valve_position_float @ 32874, heater_current_float @ 32928 — confirmed by Eurotherm 2000 Series Communications Handbook (IEEE float address calculation formula: Modbus_Address * 2 + 0x8000)

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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