The Samsung MIM-B19N Modbus Interface Module is a genuine Samsung accessory that bridges Samsung's proprietary NASA (R1/R2) communication protocol to standard Modbus RTU over RS485. It enables centralised monitoring and control of a Samsung DVM, CAC or FJM system from any Modbus master device, including Building Management Systems, PLCs, SCADA platforms, touch panels, and third-party smart controllers such as Homely.
Fitted to the outdoor unit's electrical enclosure and powered directly from the unit itself, the MIM-B19N exposes real-time operating status, temperatures, error codes and control registers for up to 48 indoor units across as many as 4 outdoor units per module. It is the standard interface required whenever a Samsung heat pump or air conditioning system needs to talk to a non-Samsung control platform.
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48
indoor units per module
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247
max Modbus network addresses
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9600 bps
Modbus RTU baud rate
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1000 m
max RS485 cable run
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DC 12V
powered from outdoor unit
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-10 to 50°C
operating range
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Qualified Installation Required
The MIM-B19N connects directly to the outdoor unit's main and sub control boards and is powered from the unit's own DC 12V supply. Installation must be carried out by a qualified service technician in accordance with Samsung's installation manual. Incorrect wiring, incorrect RS485 polarity, or an out-of-range address will prevent communication and may trigger tracking errors (E604) or address errors (E634).
Not Compatible with Samsung's Own Centralised Controllers
Once the MIM-B19N is fitted, Samsung's own upper-level controllers — On/Off controllers, Touch centralised controllers and DMS — cannot be used on the same system. The Modbus interface becomes the sole route for centralised control and monitoring.
Key Features
Modbus RTU over RS485
Standard Modbus RTU EIA485 slave device at 9600 bps, 8 data bits, 1 stop bit, even parity — compatible with any generic Modbus master.
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Wide Compatibility
Connects to any NASA-compatible Samsung DVM-S, CAC or FJM system without an additional board. RAC units (AR18–24) require the separate MIM-R10N add-on board.
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Supports Up to 48 Indoor Units
A single module can manage up to 48 indoor units and 4 outdoor units (1 main plus 3 sub units in modular installations).
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Full Read/Write Register Access
Supports Modbus function codes 03 and 04 (read) and 06 and 16 (write), exposing on/off state, mode, fan speed, set temperature, room temperature, hot water controls and error codes.
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Diagnostic LED & 7-Segment Display
Onboard Y-GRN and RED LEDs indicate outdoor unit and BMS communication activity; a 7-segment display shows error codes such as E604 (tracking error) directly on the module.
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DIP & Rotary Address Switches
Module address is set with DIP switches (SW4/SW5) and a rotary switch (SW1), giving a configurable address range of 1 to 247 across the Modbus network.
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Specification
| Communication |
| Unit connection protocol |
Samsung Control Layer Protocol (R1/R2) |
| BMS unit protocol |
Modbus RS485, 2-wire, max. 1000 m |
| Modbus communication protocol |
Modbus RTU EIA485 |
| Device type |
Slave |
| Baud rate |
9600 bps |
| Data bits |
8 |
| Stop bit |
1 |
| Parity |
Even |
| Byte order |
Big endian (MSB, LSB format) |
| Supported function codes |
Read: 03 (holding registers), 04 (input registers). Write: 06 (single register), 16 (multiple holding registers) |
| Connectivity & Capacity |
| Max connectable outdoor units |
1 (up to 4 including sub units in modular installation) |
| Max connectable indoor units |
48 per module |
| Modbus interface address range |
1 to 247 |
| Indoor unit address range |
0 to 47 |
| Electrical & Environmental |
| Power supply |
DC 12V, from outdoor unit main board (CN12) |
| Operating temperature range |
-10°C to 50°C |
| Compatible Unit Types |
| Supported connections |
DVM/CAC indoor unit, hydro kit (low/high temperature), ERV, ERV+, DVM CHILLER, FCU, FCU Kit, and EHS |
| RAC compatibility |
Requires additional MIM-R10N board for single-split wall units (AR18–24) |
| Not compatible with |
Samsung On/Off controllers, Touch centralised controllers, DMS (cannot be used alongside the Modbus interface) |
Frequently Asked Questions
What does the MIM-B19N actually do?
It is a protocol gateway. Samsung heat pumps and air conditioning systems communicate internally using Samsung's own NASA (R1/R2) protocol, which most third-party controllers and BMS platforms cannot read directly. The MIM-B19N translates that traffic into standard Modbus RTU registers over RS485, so any Modbus master can monitor and control the system.
Is this the same module used for the Homely Samsung kit?
Yes. This is the same MIM-B19N interface module supplied as part of Homely's dedicated Samsung Modbus kit. It is listed separately here for installers who already have a Homely Hub and Node, or who need it for a different Modbus master such as a BMS.
How many indoor and outdoor units can one module support?
A single MIM-B19N supports up to 48 indoor units and 4 outdoor units (1 main unit plus 3 sub units in a modular outdoor configuration).
What happens if the wiring polarity is wrong?
If the RS485 A/B polarity between the MIM-B19N and the Modbus master does not match, communication will not work. Samsung's installation manual stresses checking polarity carefully during commissioning.
Can it be used with a BMS instead of Homely?
Yes. The MIM-B19N is a standard Modbus RTU gateway and can be read by any Modbus master — BMS, PLC, SCADA or HMI/touch panel — not just Homely. Multiple modules (each with a unique address, 1–247) can sit on the same Modbus network.
What do the error codes on the 7-segment display mean?
Common codes include E6 16 (communication with all units stopped over 3 minutes), E6 15 (a specific indoor unit stopped communicating), E6 04 (tracking not completed within 10 minutes of power-on), E6 54 (EEPROM error) and E6 34 (address error).
