The IntesisBOX SM-RC2-MBS-1 (order code INMBSSAM001R100) is a Modbus gateway by Intesis (HMS Networks) that interfaces Samsung NASA commercial air conditioners — including VRF and DVM (Digital Variable Multi) systems — with Modbus RTU (EIA-485) networks. TapHome connects to the gateway via Modbus TCP using a TCP-to-RTU bridge; the gateway itself communicates with the indoor unit over Samsung’s proprietary F3/F4 Remote Controller Bus.
The template provides ON/OFF control, operating mode selection, fan speed adjustment, vane position control, thermostat with setpoint and current temperature, and error code monitoring.
This gateway is for Samsung NASA systems only (typically commercial VRF/DVM). Samsung manufactures a separate NON-NASA protocol for older residential and light-commercial units, served by the SM-RC-MBS-1 / INMBSSAM001R000 model. Verify the indoor unit’s protocol before ordering — the two variants are not interchangeable.
Hardware connection
The gateway has two plug-in terminal blocks (2 poles each):
- F3/F4 connector — connects to the Samsung indoor unit’s Remote Controller Bus (F3 and F4 terminals). Maximum bus length is 100 m (328 ft).
- EIA-485 connector (A+, B-) — connects to the Modbus RTU bus. Maximum bus length is 1,200 m (3,937 ft). Daisy-chain topology only — loop and star topologies are not permitted.
The gateway is powered directly from the Samsung F3/F4 bus — no external power supply is required. The indoor unit must be powered on for the gateway to start communicating.
The user manual states that the F3/F4 bus is polarity-sensitive while the installation sheet notes no specific polarity. The two documents contradict each other — follow the user manual as the authoritative source and observe F3/F4 polarity during commissioning. If communication fails, swap the two wires and power-cycle the gateway.
Communication may shut down if a Samsung wired remote controller is connected to the same bus without proper Main/Sub setup. Only one wired remote controller may coexist with the gateway on the F3/F4 bus, and it must be set as Main. Adding a second wired remote or any third-party controller on the same bus can halt communication.
EIA-485 bus termination
A 120 Ω termination resistor is required at each end of the EIA-485 bus. The gateway has a built-in 120 Ω resistor that can be activated via DIP switch SW4-P4. Enable it only if the gateway is at the physical end of the bus. A fail-safe biasing mechanism must be supplied by the Modbus master.
Up to 63 INMBSSAM001R100 gateways can be installed on the same Modbus RTU bus.
Enabling Modbus communication
The gateway has three DIP-switch banks: SW1 (reserved, not used), SW3 (Modbus slave address and baud rate high bits), and SW4 (temperature format, baud rate low bit, and EIA-485 termination). All changes require a full power cycle to apply.
Temperature scaling (SW4-P1) — critical for TapHome
The TapHome template divides temperature register values by 100 on read and multiplies by 100 on write. This matches the gateway’s decidegree mode (×10), where the register represents tenths of a degree — for example, 225 represents 22.5 °C. The template’s /100 factor accounts for both the ×10 gateway scaling and the internal fixed-point representation used by the import parameter.
Set SW4-P1 to ON (decidegrees ×10) during commissioning. With the default SW4-P1=OFF (degrees ×1), the gateway sends integer values like 22 for 22 °C, which the template would read as 0.22 °C — a tenfold error that makes the thermostat unusable.
| SW4 position | OFF (default) | ON |
|---|---|---|
| SW4-P1 (Temperature magnitude) | Degrees ×1 | Decidegrees ×10 — required for TapHome |
| SW4-P2 (Temperature units) | Celsius (keep) | Fahrenheit |
| SW4-P3 (Baud rate low bit) | See baud rate table | See baud rate table |
| SW4-P4 (EIA-485 termination) | No termination resistor | Internal 120 Ω termination |
Modbus slave address (SW3-P1..P6)
The slave address is encoded on SW3 pins P1..P6 as a 6-bit binary number (P1 = LSB, P6 = MSB). Valid range is 1..63; address 0 is invalid. The default factory setting is address 1 (only P1 is ON). The full address table is printed on the installation sheet.
Baud rate (SW3-P7..P8 + SW4-P3)
The baud rate is encoded on three pins across two DIP banks. The default is 9600 bps — which matches the TapHome template’s expectation. Supported rates: 2400, 4800, 9600, 19200, 38400, 57600, 76800, 115200 bps.
The gateway uses an 8N2 frame by default (8 data bits, no parity, 2 stop bits) and auto-detects 8N1 if the master uses it — no manual configuration is required on the Modbus side.
Enabling on the AC side
The gateway is a transparent bridge — no configuration is required on the Samsung indoor unit itself beyond wiring it correctly to the F3/F4 bus. The indoor unit must be powered on for the F3/F4 bus to be energized, which in turn powers the gateway.
If the target installation uses ambient temperature from the Modbus side (register H:22) instead of the indoor unit’s return-air sensor, the Samsung indoor unit must be configured to use the Remote Controller temperature as its control-loop reference. Refer to the Samsung installation manual for the option code. This register is not exposed by the current TapHome template.
TapHome connection
Since the IntesisBOX communicates via Modbus RTU (EIA-485), a Modbus TCP-to-RTU bridge is required between TapHome Core and the EIA-485 bus. TapHome connects to the bridge over the local network using Modbus TCP on port 502.
When importing the template in TapHome, provide:
- IP Address — the TCP-to-RTU bridge’s IP on the local network (default: 192.168.0.1)
- Slave ID — the gateway’s Modbus address set via SW3 DIP switches (default: 1)
Assign a static IP address to the TCP-to-RTU bridge in the router’s DHCP settings to prevent the address from changing after a power cycle.
Device capabilities
The template exposes 6 devices communicating over holding registers H:0 through H:11. Control registers (H:0–H:4) are polled every 2.5 s; the error code (H:11) is polled every 15 s.
ON/OFF
Simple switch that turns the AC unit on or off. Reads and writes register H:0 (Bool). 0 = Off, 1 = On.
Mode
Operating mode selector with the five standard Samsung NASA modes:
| Value | Mode |
|---|---|
| 0 | Auto |
| 1 | Heat |
| 2 | Dry |
| 3 | Fan |
| 4 | Cool |
The template defines 10 positions (values 0–9). Only values 0–4 are documented by the manufacturer — values 5–9 are reserved NASA pass-through slots without documented semantics and should not be used in practice. Reads and writes register H:1 (Int16).
Fan Speed
Fan speed selector with the five standard Samsung NASA speeds:
| Value | Speed |
|---|---|
| 0 | Auto |
| 1 | Low |
| 2 | Mid |
| 3 | High |
| 4 | Turbo |
The template defines 10 positions (values 0–9). The number of actually available fan speeds depends on the connected indoor unit model — the manual documents only values 0–4. Reads and writes register H:2 (Int16).
Vane Position
Vertical vane (up/down louver) position control:
| Value (template) | Position |
|---|---|
| 0 | Auto (Swing Off) |
| 5 | Swing On |
| 1–4, 6–9 | Samsung NASA pass-through (Position 1 Horizontal, Vertical, Swirl, etc.) |
The user manual guarantees only two values for this register: 0 (Swing Off / Auto) and 10 (Swing On). The template remaps Swing On to a contiguous value (5) for the multi-value switch UI and adds Samsung-specific labels (Position 1 Horizontal, Vertical, Swirl) that are passed through the NASA protocol. These extra positions may or may not work depending on the indoor unit model — most installations should use only Auto and Swing On.
Reads and writes register H:3 (Int16).
Thermostat
Temperature setpoint (register H:4, read/write) and current reference temperature (register H:5, read-only). The template divides read values by 100 and multiplies written values by 100 — this scaling requires SW4-P1=ON (decidegree mode) on the gateway, as described in the Temperature scaling section above.
Setpoint range is 18–30 °C in Cool mode and 16–30 °C in Heat mode (gateway-enforced; indoor-unit limits may be tighter). The reference temperature reflects the Samsung indoor unit’s active control-loop sensor — by default its own return-air sensor, or the remote controller’s sensor, or an external value written to register H:22 if that feature has been enabled on the indoor unit.
Error Code
Read-only numeric value from register H:11. Key values:
| Value | Meaning |
|---|---|
| 0 | No error |
| 65535 (-1) | Communication error between gateway and AC indoor unit |
| Other | Samsung NASA error code |
Common Samsung NASA error categories include:
- 1xx — Communication and indoor sensor errors (e.g. 101 indoor communication, 121 indoor temperature sensor)
- 2xx — Configuration and outdoor communication errors (e.g. 201 unit mismatch, 202 indoor/outdoor comms)
- 4xx–5xx — Outdoor unit protection errors (compressor, PFC, DC link, heat sink)
- 6xx — Wired remote controller configuration errors
See Section 7 of the user manual for the complete error code table with over 50 documented codes.
Troubleshooting
No Modbus communication
- Verify that the indoor unit is powered on — the gateway is bus-powered from F3/F4 and cannot start without it.
- Check the green LED (L1): normal operation is a short 100 ms flash every 2 s. A 500 ms ON / 500 ms OFF blink indicates a communication error.
- Confirm the slave address configured in TapHome matches the SW3 DIP switch setting on the gateway.
- Verify the baud rate (default 9600 bps, 8N2) matches the TCP-to-RTU bridge configuration.
- Ensure the TCP-to-RTU bridge is reachable on the same network as TapHome Core and that port 502 is not blocked.
- If F3/F4 communication fails, try swapping the two wires — the user manual describes the bus as polarity-sensitive.
Error code 65535 persistent
This indicates the gateway cannot communicate with the Samsung indoor unit over the F3/F4 bus. Check F3/F4 wiring, verify the indoor unit is powered on, and confirm no conflicting wired remote controller is installed on the same bus without correct Main/Sub configuration.
Temperature values are 10× wrong
The TapHome template divides register values by 100. If the gateway is left in its default SW4-P1=OFF state (degrees ×1), temperatures appear 10× smaller than reality (22 °C shows as 0.22 °C). Set SW4-P1=ON (decidegrees ×10) and power-cycle the gateway.
L2 red LED pulsing
A 3 s pulse on the red LED (L2) indicates under-voltage on the F3/F4 bus. Verify the indoor unit is powered and the F3/F4 cable is securely connected with no voltage drop across long runs.
Mode or fan speed changes not applied
Some values (Mode 5–9, Fan Speed 5–9, Vane positions other than Auto/Swing On) are not documented by the manufacturer and may be silently ignored by the indoor unit. Use only the documented values (Mode 0–4, Fan 0–4, Vane 0 or 5).
DIP switch changes ignored
DIP switch changes on SW3 or SW4 require a full power cycle of the gateway. Since the gateway is bus-powered, disconnect the F3/F4 cable briefly or power-cycle the indoor unit to restart it.
