The IntesisBOX LG-RC-MBS-1 (order code INMBSLGE001R000, legacy LG-RC-MBS-1) is a Modbus gateway by Intesis (HMS Networks) that interfaces LG air conditioners — VRF / Multi V indoor units and many commercial / RAC indoor units sharing the LG control protocol — with Modbus RTU (EIA-485) networks. The gateway attaches to the LG BYR 3-wire bus — the same bus used by the LG wired remote controller — and supports one indoor unit per gateway.
TapHome connects to the gateway via Modbus TCP through a TCP-to-RTU bridge — the gateway itself is a native Modbus RTU slave. The template provides ON/OFF control, operating mode selection, fan speed adjustment, vertical vane position control, thermostat with setpoint and current temperature, and error code monitoring. Per-model compatibility for specific LG indoor units can be verified using the Intesis HVAC Compatibility Tool.
Hardware connection
The gateway has two plug-in screw terminal blocks:
- BYR bus (3 poles — terminals B, Y, R) — connects to the LG BYR bus on the indoor unit’s “TO REMOTE CONTROL UNIT” socket, in parallel with any LG wired remote controller.
- EIA-485 bus (2 poles — terminals A+, B−) — connects to the Modbus RTU bus where TapHome’s TCP-to-RTU bridge sits as Modbus master.
The gateway is powered directly from the AC indoor unit via the LG BYR bus (12 VDC, 0.72 W) — no external power supply is needed. The AC indoor unit must therefore be connected to mains for the gateway to communicate.
System topology
Up to 63 LG-RC-MBS-1 gateways can share the same Modbus RTU EIA-485 bus, each addressed via SW3-P1..P6. Each gateway connects to one LG AC indoor unit on its own BYR bus (this is the single-IDU “RC” variant — for multi-IDU LG installations on the outdoor PI485 bus, a different gateway model is required). TapHome (acting as Modbus master through a TCP-to-RTU bridge) sees every gateway as a separate Modbus slave.
BYR-bus wiring
The BYR bus is a 3-wire bus with no polarity sensitivity — terminals can be connected without minding wire order, but the wire colour ↔ pin mapping at the AC indoor unit’s “TO REMOTE CONTROL UNIT” socket is:
| Terminal | Wire colour | Function |
|---|---|---|
| R | Red | Power (+12 VDC) |
| Y | Yellow | Data |
| B | Black | GND |
Two installation scenarios are supported:
- Wired remote control available — connect the gateway as Slave (SW1-P1 = OFF) in parallel with the LG wired remote controller, which acts as Master. Both share the BYR bus.
- No wired remote control available — connect the gateway as Master (SW1-P1 = ON) directly to the BYR bus. If a controller is added later, it must be configured as Slave.
Maximum BYR bus length is 50 m / 164 ft. The cable can be either the cable supplied by LG or any unshielded 3-wire cable (keep wire order to preserve the colour ↔ pin mapping). Solid or stranded wires are accepted, 0.5–2.5 mm² for single-core, 0.5–1.5 mm² for two-core; three-core ferrules are not permitted.
Disconnect the AC unit from mains power before opening the indoor unit. Type A LG units do not allow installing both a Remote Controller and the gateway together — only Type B units support parallel installation. The machine type is set on the gateway via SW1-P2 and must match the actual LG model. Keep the BYR cable away from electrical wires and ground wires — do not bundle them together.
EIA-485 wiring and termination
The EIA-485 bus polarity must be respected: A+ to A+, B− to B− across all devices on the bus. Maximum EIA-485 bus length is 1,200 m / 3,937 ft. Loop and star topologies are not allowed — the bus must be wired as a daisy chain.
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 sits at one end of the bus. A fail-safe biasing mechanism is required and must be supplied by the Modbus master (typically built into the TCP-to-RTU bridge).
Configuration
The LG-RC-MBS-1 is configurable via on-board DIP switches and via Modbus registers. Default settings (slave address 1, 9600 bps, all other DIP switches OFF) work out of the box on a typical Type B installation, so usually only the slave address, the machine type (SW1-P2) and the EIA-485 termination need to be reviewed. Every DIP-switch change requires a power cycle of the gateway to take effect — that is, disconnecting the AC indoor unit from mains so the BYR bus loses its 12 VDC supply, then reconnecting after a few seconds.
DIP-switch layout
The gateway has three DIP-switch banks: SW1 (4 positions, AC indoor-unit features), SW3 (8 positions, Modbus slave address + baud rate) and SW4 (4 positions, temperature format + EIA-485 termination).
Enabling Modbus communication
The LG-RC-MBS-1 ships with Modbus RTU communication enabled by default — there is no menu navigation or web UI to activate it. Setting up Modbus is a matter of selecting the correct slave address, baud rate and frame format on the DIP switches.
SW1 — AC indoor-unit features
| Position | Default (OFF) | ON |
|---|---|---|
| SW1-P1 | Slave — gateway is BYR-bus Slave (an LG wired remote controller must be present, configured as Master). | Master — gateway is BYR-bus Master (no LG wired controller present, or if present it must be Slave). |
| SW1-P2 | Error Type B — machine must be Type B. | Error Type A — machine must be Type A. |
| SW1-P3 | Minimum ambient temperature not applied. | Minimum ambient temperature applied. |
| SW1-P4 | Keep in this position (default). | Reserved — do not turn ON. |
SW1-P2 selects the LG Error Type (machine type) — A or B — and must match the actual LG indoor unit model. Use the Intesis compatibility tool to look up the type for a specific LG model. Type A LG units cannot host both an LG Remote Controller and the gateway on the same BYR bus; Type B units can. SW1-P3 is a safety limiter that prevents the AC unit from running below a manufacturer-defined minimum ambient temperature — leave OFF unless the application explicitly requires it.
SW3 — Modbus slave address (P1..P6) and baud rate (P7..P8)
The slave address is binary-encoded across SW3-P1..P6 with P1 = LSB (P1=1, P2=2, P3=4, P4=8, P5=16, P6=32). Range: 1..63. Common examples:
| Address | P1 | P2 | P3 | P4 | P5 | P6 |
|---|---|---|---|---|---|---|
| 1 (default) | ON | OFF | OFF | OFF | OFF | OFF |
| 2 | OFF | ON | OFF | OFF | OFF | OFF |
| 3 | ON | ON | OFF | OFF | OFF | OFF |
| 10 | OFF | ON | OFF | ON | OFF | OFF |
| 63 (max) | ON | ON | ON | ON | ON | ON |
Baud rate is selected by SW3-P7, SW3-P8 and SW4-P3 combined:
| SW3-P7 | SW3-P8 | SW4-P3 | Baud rate |
|---|---|---|---|
| OFF | OFF | OFF | 2400 bps |
| ON | OFF | OFF | 4800 bps |
| OFF | ON | OFF | 9600 bps (default) |
| ON | ON | OFF | 19200 bps |
| OFF | OFF | ON | 38400 bps |
| ON | OFF | ON | 57600 bps |
| OFF | ON | ON | 76800 bps |
| ON | ON | ON | 115200 bps |
Default frame format is 8N2 (8 data bits, no parity, 2 stop bits). 8N1 is also auto-detected — no manual setting needed.
SW4 — Temperature format and EIA-485 termination
| Position | Default (OFF) | ON |
|---|---|---|
| SW4-P1 | Temperature in degrees ×1 (e.g. 22 = 22 °C). | Temperature in decidegrees ×10 (e.g. 220 = 22.0 °C). |
| SW4-P2 | Celsius. | Fahrenheit. Cannot be combined with ×10. |
| SW4-P3 | — | See SW3 baud rate table above. |
| SW4-P4 | No on-board EIA-485 termination. | Internal 120 Ω termination connected. |
The user manual lists the default for SW4-P1 as “x1 (Celsius)” in the DIP-switch table but elsewhere refers to “x10 (decicelsius, default)” as the gateway’s baseline temperature representation. The TapHome XML template applies a
/100divisor (raw value ×100) to the thermostat registers — verify the actual SW4-P1 setting and observed values at commissioning, and adjust the divisor in the template scripts if setpoints are reported 10× or 100× too small.
Importing the template in TapHome
Since the gateway communicates over Modbus RTU, 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. When importing the template, provide:
- IP Address — the bridge’s IP on the local network (default:
192.168.0.1) - Slave ID — the gateway’s Modbus address set via SW3-P1..P6 (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. If the bridge supports multiple slave addresses on the same EIA-485 line, you can chain up to 63 LG-RC-MBS-1 gateways on a single bus — one per LG indoor unit.
Device capabilities
The template exposes 6 devices polled from holding registers H:0 through H:11. Implemented Modbus functions: 3 (Read Holding Registers), 4 (Read Input Registers), 6 (Write Single Register), 16 (Write Multiple Registers — limited to 1 register per request).
ON/OFF
Simple switch to turn the AC unit on or off. Reads and writes register H:0 (Bool). Poll interval: 2.5 s.
Mode
Operating mode selector with the 5 modes documented by Intesis:
| Value | Mode |
|---|---|
| 0 | Auto |
| 1 | Heat |
| 2 | Dry |
| 3 | Fan |
| 4 | Cool |
The template defines 10 positions (values 0–9). Values 5–9 are placeholder slots that are not documented in the user manual and will not be reachable on real LG indoor units. Reads and writes register H:1 (Int16). Poll interval: 2.5 s.
Fan Speed
Fan speed selector. The LG manual documents the following encoding for the BYR bus:
| Manual value | Speed |
|---|---|
| 0 | Auto |
| 1 | Position 1 |
| 2 | Position 2 |
| 3 | Position 3 |
| 4 | Position 4 |
| 5 | Position 5 |
| 6 | Position 6 |
| 7 | Position 7 |
The TapHome template reorders the fan-speed labels relative to the LG register encoding. Selecting template slot 2 (labelled “Position 5”) writes register value 2 to the indoor unit, which actually corresponds to Position 2 per the manual — and so on for slots 3–5. The user-facing labels for Auto, Position 1, Position 6 and Position 7 line up with the manual; the rest are mislabelled. The natural Position 1 < 2 < 3 < … ordering is therefore broken in the UI. Register H:21 (read-only, not exposed in the template) reports the maximum number of fan speeds the connected unit actually supports — useful to know how many slots are physically reachable on a given LG model. Verify the actual fan-speed mapping at commissioning.
Reads and writes register H:2 (Int16). Poll interval: 2.5 s.
Vane Position
Vertical (U/D) vane position control. The user manual documents the following encoding:
| Manual value | Position |
|---|---|
| 0 | No Swing |
| 1 | Position 1 |
| 2 | Position 2 |
| 3 | Position 3 |
| 4 | Position 4 |
| 10 | Swing |
| 11 | Swirl |
The TapHome template remaps Swing onto register value 5 and Swirl onto register value 9 to keep the multi-value switch range contiguous. The LG user manual reserves register value 10 for Swing and value 11 for Swirl — selecting template Swing (slot 5) actually writes register value 5 to the indoor unit, which is undocumented for the vertical-vane register H:3. Verify at commissioning whether the indoor unit silently accepts these values or whether Swing/Swirl need to be mapped explicitly to 10 / 11. The template also exposes additional slots (Position 4 (Vertical), Position 6, Position 7) that are not documented in the manual for the vertical vane.
Reads and writes register H:3 (Int16). Poll interval: 2.5 s.
Thermostat
Temperature setpoint (register H:4, read/write) and current reference temperature (register H:5, read-only). The setpoint range on LG units is 16–30 °C (61–86 °F). The reference temperature reflects the indoor unit’s own control-loop sensor (return-path thermistor or, when so configured at install time, the wired remote controller’s thermistor); it returns −32768 (0x8000) when no value has yet been received from the BYR bus.
The TapHome template applies a /100 divisor to the temperature registers, but the LG-RC-MBS-1 user manual only documents three temperature modes selectable via SW4-P1 / SW4-P2: ×1 Celsius, ×10 decicelsius (default per documentation), or Fahrenheit. There is no documented ×100 (centi-degree) mode for this gateway. The TapHome integration assumes the gateway is configured per its default — values can be tuned in the template scripts if scaling differs in your installation. If you observe setpoints reported as ~0.22 °C instead of 22 °C, verify the raw register values with the TapHome Modbus debug tool and adjust either the gateway’s DIP switches or the template scaling accordingly.
Poll interval: 2.5 s.
Error Code
Read-only numeric value from register H:11. Key values:
| Value | Meaning |
|---|---|
| 0 | No error |
| 65535 | Communication error between the Intesis gateway (or remote controller) and the AC unit |
| Other | LG fault code — see categories below |
The full error-code table is published in the user manual (section 7) and the Modbus error code matches the value displayed by the LG wired remote controller. Selected categories:
| Range | Category examples |
|---|---|
| 1–12 | Indoor unit sensor / motor / EEPROM faults (room air, pipe in/out, drain pump, BLDC motor, HEX middle-point sensor, heater terminal block) |
| 17–22 | Indoor unit communication and AC input current faults (outlet/return air sensor, sub-PCB ↔ main-PCB communication, IPM, AC over-current) |
| 23–35 | DC link voltage, high/low pressure switch, compressor start, PSC/PFC, discharge temperature, pressure-ratio anomalies |
| 39–62 | Inverter / outdoor PCB sensor faults, missing or reverse phase, combination ratio, EEPROM, outdoor pipe / IPM temperature |
| 67–88 | Fan motor / DC link / hall sensor / PCB EEPROM faults |
| 104–116 | Sub-unit communication, fan PCB, liquid pipe / sub-cooling sensor faults |
| 145–238 | External / hydro-kit PCB sensor faults, 4-way valve, HEX, constant-speed compressor current, modem communication, Heat Recovery (HR) unit faults |
The Modbus error code matches the value shown on the LG wired remote controller’s display — useful for cross-checking faults from the TapHome side without physical access to the controller. If the value returned is
65535, the gateway has lost communication with the LG indoor unit on the BYR bus — see Troubleshooting below.
Poll interval: 15 s (vs 2.5 s for the control registers).
Troubleshooting
No Modbus communication
- Verify the AC indoor unit is powered on — the gateway requires 12 VDC supplied via the LG BYR bus.
- Check the LED indicators: L1 + L2 pulse together (5 s ON) at startup; L1 flashing (100 ms ON / 1900 ms OFF) indicates normal operation; L1 blinking (500 ms ON / 500 ms OFF) indicates a communication error with the AC unit; L2 pulsing (3 s ON) indicates undervoltage; alternating L1/L2 blink (500 ms / 500 ms) indicates a flash checksum failure.
- Confirm the slave address in TapHome matches the SW3-P1..P6 binary setting on the gateway.
- Ensure the TCP-to-RTU bridge is on the same network as TapHome Core and the bridge’s serial settings match SW3 baud rate (default 9600 bps, 8N2 — 8N1 is auto-detected).
- Verify the EIA-485 polarity — A+ / B− must be consistent across all devices on the bus.
- Check that 120 Ω termination is enabled at both ends of the EIA-485 bus (one end is typically the bridge, the other is the gateway via SW4-P4 = ON).
Error code 65535 continuously
This indicates the gateway cannot communicate with the LG AC indoor unit over the BYR bus. Check:
- B / Y / R wires are connected at all three terminals at both ends — the bus has no polarity sensitivity, but all three wires must be present (R = power, Y = data, B = GND).
- The AC indoor unit is powered (mains).
- If an LG wired remote controller is also present, confirm only one device (gateway or controller) is configured as Master — verify SW1-P1 against the topology.
- BYR bus length does not exceed 50 m.
- For Type A LG indoor units, a wired remote controller and the gateway cannot coexist — confirm SW1-P2 matches the actual machine type and that no remote controller is wired to the same bus on Type A units.
Master/Slave conflict on the BYR bus
If the LG wired remote controller and the gateway are both configured as Master, the BYR bus will collide and one or both devices will stop responding. Set SW1-P1 to OFF (gateway as Slave) whenever an LG wired controller is present on the same bus, and to ON (gateway as Master) only when no LG wired controller is connected. The Master/Slave state is also exposed (read/write) on register H:98 — this register is not used by the TapHome template, but it can be queried with a Modbus diagnostic tool to confirm the gateway’s current role at runtime.
Temperature values are incorrect
The template uses a /100 divisor on registers H:4 and H:5. The LG-RC-MBS-1 supports three temperature representations on the BYR side — ×1 Celsius (SW4-P1 OFF, SW4-P2 OFF), ×10 decicelsius (SW4-P1 ON, SW4-P2 OFF), and Fahrenheit (SW4-P2 ON). With a /100 scaling on the TapHome side, a setpoint of 22 °C will be reported as 0.22 °C in ×1 mode, or as 2.2 °C in ×10 mode. Use the Modbus debug tool in TapHome to read raw register values and compare with the expected setpoint, then either reconfigure the gateway DIP switches or adjust the divisor in the template scripts.
Setpoint differs from the LG remote controller display
When the Virtual Temperature mechanism is in use (an external ambient reference written to register H:22, gateway acting as Slave), the indoor unit applies an adjusted internal setpoint following S_AC = S_u − (T_u − T_AC). The LG remote controller may then display a different number than the user-requested setpoint (register H:4). This is expected behaviour — register H:23 (real temperature setpoint, not exposed in the template) reports the value actually applied to the indoor unit. To make the indoor unit use the wired remote controller’s thermistor as control-loop reference, the AC unit must be configured by an LG-authorized installer at commissioning (the option “thermostat sensor in the Remote Controller” must be activated) — this is not changeable from the Modbus side.
DIP-switch change not taking effect
Every DIP-switch change requires a power cycle of the gateway to apply. Power cycling means disconnecting the AC indoor unit from mains (which removes the 12 VDC supply on the BYR bus) and reconnecting after a few seconds. Modifying DIP switches while the gateway is powered will not change the active configuration.
