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Actuator / valve (damper and valve actuator) · Modbus register map
Belimo Air/water actuators with Modbus RTU (..24A-MOD) Modbus register map
Updated 28 October 2026
Belimo's standard damper and valve actuators in the -MOD version speak Modbus RTU on RS-485 directly. The map is small and flat: a position setpoint, an override, position feedback and an optional sensor input in registers 1-13, then identity, fault flags, Min/Max limits, the bus watchdog and the setpoint source from register 100 up. Everything is a 16-bit unsigned value.
This page lists 22 Modbus registers for the Belimo Air/water actuators with Modbus RTU (..24A-MOD) — 11 writable — with the table, 0-based wire address, data type, word order, scale, units and access of each, re-typed from Belimo’s own free documentation (linked below) and checked against it.
- Manufacturer
- Belimo
- Model
- Air/water actuators with Modbus RTU (..24A-MOD)
- Equipment type
- Actuator / valve (damper and valve actuator)
- Registers
- 22 (11 writable)
- Transport
- Modbus RTU
- Default unit ID
- 1
- Default serial
- 38400 baud, 8N2
- Documented addressing
- 1-based (subtract 1 for the wire address)
- Also known as
- LM24A-MOD, NM24A-MOD, SM24A-MOD, GM24A-MOD, LMC24A-MOD, NMC24A-MOD, NR24A-MOD, LR24A-MOD, NV24A-MOD, NVK24A-MOD, LF24A-MOD, NF24A-MOD, NRF24A-MOD, LRF24A-MOD, LH24A-MOD, SH24A-MOD
Integration notes: Belimo Air/water actuators with Modbus RTU (..24A-MOD)
Wire to the RS-485 terminals, set address and frame with the Belimo Assistant app (or the Address button quick-addressing), then write the position in 0.01 % to register 1 (wire address 0) and poll registers 5 and 105. Leave Setpoint source (No. 119) at Bus, its default.
Minimum registers to map
Addresses are 0-based wire addresses. Enough to monitor and run the unit; map more as the job needs.
| Register | Name | Type | Why | Access |
|---|---|---|---|---|
| HR 0 | Setpoint | UINT16 | Position setpoint, 0.01 % | Read/write |
| HR 1 | Override control | UINT16 | Override (open/close/min/mid/max) | Read/write |
| HR 4 | Relative position | UINT16 | Relative position feedback | Read |
| HR 104 | Malfunction and service information | BITMAP16 | Fault and service flags | Read |
| HR 118 | Setpoint source | UINT16 | Setpoint source must be Bus | Read/write |
| HR 108 | Bus fail position | UINT16 | Bus fail position | Read/write |
| HR 109 | Timeout for bus watchdog | UINT16 | Bus watchdog timeout | Read/write |
Enable Modbus control & writes
Modbus is active out of the box on -MOD actuators; Setpoint source (No. 119) defaults to Bus. Address (1-247), baud rate and frame are set with the Belimo Assistant 2 app or tool, and the address can also be set with the Address and Adaption buttons (see the product datasheet).
Communication loss & watchdog
Not monitored by default. Set Bus fail position (No. 109) and Timeout for bus watchdog (No. 110, 0-3600 s; 0 = off, 120 s default once a fail position is set). If neither No. 1 nor No. 2 is written within the timeout, the actuator goes to the fail position and bit 10 of No. 105 is set. In hybrid mode (Setpoint source = Analog) bus monitoring is not active.
Byte order & addressing
- The No. column is 1-based; subtract 1 for the wire address (setpoint = address 0).
- Min and Max must stay at least 20 % apart (Min <= Max - 20 %, Max >= Min + 20 %).
- Registers that a device or its settings don't support read 65535.
Network setup
- Factory frame is 38400 baud, 8 data bits, no parity, 2 stop bits (1-8-N-2), address 1.
- Supported frames: 1-8-N-2, 1-8-N-1, 1-8-E-1, 1-8-O-1; baud 9600-115200.
- Up to 32 nodes per segment without a repeater; terminate the bus ends with 120 ohm.
Watch out for
- Don't write the persistent registers (No. 101 and up) on every poll cycle - they live in non-volatile memory.
- Fast open / Fast close overrides add mechanical wear; Belimo suggests keeping them for events like frost protection.
Belimo Air/water actuators with Modbus RTU (..24A-MOD) Modbus registers
Address = 0-based wire address (the documented number is shown under it when it differs) · Order: ABCD = high word first, CDAB = low word first · Scale: engineering value = raw × scale.
| Table | Address | Name | Description | Type | Order | Scale | Units | Access | Values / bits |
|---|---|---|---|---|---|---|---|---|---|
| HR | 0doc 1 | Setpoint | Position setpoint 0-100 %, scaled between Min (No. 106) and Max (No. 107). | UINT16 | × 0.01 | % | Read/write | ||
| HR | 1doc 2 | Override control | Forces a fixed position instead of the setpoint. | UINT16 | Read/write | 0 = None; 1 = Open; 2 = Close; 3 = Min; 4 = Mid; 5 = Max; 6 = Fast open; 7 = Fast close | |||
| HR | 2doc 3 | Command | Starts a service function; reads back 0 once accepted. 4 clears No. 105. | UINT16 | Read/write | 0 = None; 1 = Adaption; 2 = Test; 3 = Sync; 4 = Reset | |||
| HR | 3doc 4 | Actuator type | UINT16 | Read | 0 = Actuator not connected; 1 = Air / water; 2 = VAV / EPIV; 3 = Fire; 4 = Energy Valve; 5 = 6-way EPIV | ||||
| HR | 4doc 5 | Relative position | UINT16 | × 0.01 | % | Read | |||
| HR | 5doc 6 | Absolute position | Degrees for rotary actuators, mm for linear actuators. | UINT16 | ° / mm | Read | |||
| HR | 8doc 9 | Sensor 1 value | Raw reading of sensor input 1; meaning and scale follow No. 108 (see notes). | UINT16 | Read | ||||
| HR | 12doc 13 | Analog setpoint | Setpoint seen on the 0-10 V input when Setpoint source = Analog. | UINT16 | × 0.01 | % | Read | ||
| HR | 99doc 100 | Bus termination | Shows whether the built-in 120 ohm terminator is on (set with the tool). | UINT16 | Read | 0 = Inactive; 1 = Active | |||
| HR | 100doc 101 | Series number 1st part | First block of the serial number on the housing label. | UINT16 | Read | ||||
| HR | 101doc 102 | Series number 2nd part | Second block of the serial number. | UINT16 | Read | ||||
| HR | 102doc 103 | Series number 4th part | Fourth block of the serial number (the third is not exposed). | UINT16 | Read | ||||
| HR | 103doc 104 | Firmware version | Bus module firmware; 302 means version 3.02. | UINT16 | Read | ||||
| HR | 104doc 105 | Malfunction and service information | Bit-coded fault and status flags; clear with Command = 4. | BITMAP16 | Read | bit 1 = Mechanical travel increased (moved outside adapted range); bit 2 = Actuator cannot move (overload / blocked); bit 8 = Internal activity (test run, adaption); bit 9 = Gear train disengaged (manual override pressed); bit 10 = Bus watchdog triggered | |||
| HR | 105doc 106 | Min | Lower position limit; must stay at least 20 % below Max. Default 0. | UINT16 | × 0.01 | % | Read/write | ||
| HR | 106doc 107 | Max | Upper position limit; must stay at least 20 % above Min. Default 100 %. | UINT16 | × 0.01 | % | Read/write | ||
| HR | 107doc 108 | Sensor 1 type | What is wired to sensor input 1; restart may be needed after a change. | UINT16 | Read/write | 0 = None; 1 = Active; 2 = Passive_1K; 3 = Passive_20K; 4 = Switch; 5 = PT1000_C; 6 = NI1000_C; 7 = NTC10K2_C; 8 = PT1000_F; 9 = NI1000_F; 10 = NTC10K2_F | |||
| HR | 108doc 109 | Bus fail position | Where the actuator goes when the bus watchdog expires. | UINT16 | Read/write | 0 = None / last setpoint; 1 = Fast close; 2 = Fast open; 3 = Mid position (parametrised) | |||
| HR | 109doc 110 | Timeout for bus watchdog | 0 disables; defaults to 120 s once a bus fail position is set. | UINT16 | s | Read/write | |||
| HR | 118doc 119 | Setpoint source | Bus = No. 1 drives the actuator; Analog = 0-10 V on wire 3. Default Bus. | UINT16 | Read/write | 0 = Analog; 1 = Bus | |||
| HR | 189doc 190 | Fail-safe bridging time | Delay before the fail-safe move after power loss (electronic fail-safe types only). | UINT16 | s | Read/write | |||
| HR | 190doc 191 | Fail-safe position | Position taken on power loss (electronic fail-safe types; knob on 'Tool'). | UINT16 | × 0.01 | % | Read/write |
Notes on this map
- Belimo states that all register values are unsigned 16-bit integers; a register that does not apply to the device or its settings reads 65535.
- Sensor 1 value (No. 9) changes meaning with Sensor 1 type (No. 108): mV for Active, ohms for the passive types, 0/1 for Switch (scale 1), and 0.1 °C or 0.1 °F for the PT1000/NI1000/NTC10K2 types. It is listed raw (scale 1); multiply by 0.1 yourself for the temperature types.
- Writable registers above No. 100 are stored in non-volatile memory; Belimo says not to write them on a regular basis.
- No. 190/191 exist only on electronic fail-safe actuators; other types return 65535.
- Registers 7, 8, 10-12 and 111-118 are unused in this actuator range and are not listed.
- Read Discrete Inputs (FC 2) can also read the bits of No. 105: start bit address = 104 x 16 = 1664.
Check it against the live device. A register map tells you what the controller can expose; the unit in front of you may differ by firmware or options. Read a few registers and compare them with the unit’s own display; for a 32-bit value the float and byte-order decoder shows all four word orders at once, so a wrong word order or scale is obvious. New to this? Read what a register map is and why addresses are off by one.
Questions about the Belimo Air/water actuators with Modbus RTU (..24A-MOD)
What Modbus registers does the Belimo Air/water actuators with Modbus RTU (..24A-MOD) have?
This map lists 22 registers: 22 holding registers. 11 of them can be written. Registers vary with firmware, options and configuration, so confirm against the device.
Are the Belimo Air/water actuators with Modbus RTU (..24A-MOD) Modbus addresses 0-based or 1-based?
The manufacturer's document numbers registers 1-based (subtract 1 for the wire address). Every address on this page is the 0-based wire address you put in the request; the documented number is shown under it where it differs. Belimo prints each register twice: 'No.' counts from 1 and 'Address' from 0, and the documented value here is the No. column. Register No. 1 (setpoint) is wire address 0. Every value sits in one flat table, so holding-register reads (FC 3) and writes (FC 6/16) reach everything; FC 4 input-register reads of the same addresses also work.
What are the minimum Modbus registers to integrate the Belimo Air/water actuators with Modbus RTU (..24A-MOD)?
Start with HR 0 Setpoint (Position setpoint, 0.01 %); HR 1 Override control (Override (open/close/min/mid/max)); HR 4 Relative position (Relative position feedback); HR 104 Malfunction and service information (Fault and service flags); HR 118 Setpoint source (Setpoint source must be Bus); HR 108 Bus fail position (Bus fail position); HR 109 Timeout for bus watchdog (Bus watchdog timeout).
How do I enable Modbus control of the Belimo Air/water actuators with Modbus RTU (..24A-MOD)?
Modbus is active out of the box on -MOD actuators; Setpoint source (No. 119) defaults to Bus. Address (1-247), baud rate and frame are set with the Belimo Assistant 2 app or tool, and the address can also be set with the Address and Adaption buttons (see the product datasheet).
What happens when the Belimo Air/water actuators with Modbus RTU (..24A-MOD) loses Modbus communication?
Not monitored by default. Set Bus fail position (No. 109) and Timeout for bus watchdog (No. 110, 0-3600 s; 0 = off, 120 s default once a fail position is set). If neither No. 1 nor No. 2 is written within the timeout, the actuator goes to the fail position and bit 10 of No. 105 is set. In hybrid mode (Setpoint source = Analog) bus monitoring is not active.
Where is the official Belimo Air/water actuators with Modbus RTU (..24A-MOD) Modbus documentation?
The source is Modbus Interface Description - Air/water actuators (General actuators for air and water) (Edition 2026-05 / V3.08), revision 2026-05, published free by Belimo at https://www.belimo.com/mam/general-documents/system_integration/Modbus/belimo_Modbus-Register_AirWater_V3_8_en-gb.pdf.
More Belimo Modbus register maps
- Actuator / valve (pressure-independent characterised control valve)
Belimo 2-way EPIV DN 15-50 (Version 4.2) Modbus RTU
Belimo 2-way EPIV DN 15-50 Version 4 (EP..R2+(K)BAC) on Modbus RTU, per interface description edition 2025-09 / V4.2.
Also known as: EP..R2+BAC, EP..R2+KBAC, Electronic pressure-independent valve - Actuator / valve (6-way pressure-independent change-over valve)
Belimo 6-way EPIV Modbus RTU (EP..R-R6+BAC)
Belimo 6-way EPIV EP..R-R6+BAC on Modbus RTU, per 6-way EPIV Modbus Register en-gb 2024-01 (general notes dated 16.12.2019).
Also known as: EP..R-R6+BAC, 6-way pressure-independent valve - Actuator / valve (pressure-independent control valve with energy metering)
Belimo Energy Valve DN 15-50 (Version 4) Modbus RTU / TCP
Belimo Energy Valve Version 4, DN 15-50 (EV..R2+(K)BAC, EV..R2+MID, EV..R3+BAC), per Energy Valve Modbus interface description en-gb 2023-08.
Also known as: EV..R2+BAC, EV..R2+KBAC, EV..R2+MID, EV..R3+BAC, Energy Valve 4
Source: Modbus Interface Description - Air/water actuators (General actuators for air and water) · Edition 2026-05 / V3.08 · rev. 2026-05. Register numbers, types, scaling and units are reproduced as published; descriptions are our own.