The IntesisBOX DK-RC-MBS-1 (current order code INMBSDAI001R000, replaced by IN485DAI001R000 — same hardware, new SKU) is a Modbus gateway by Intesis (HMS Networks) that interfaces Daikin VRV and SKY Air commercial air conditioning systems with Modbus RTU (EIA-485) networks. Unlike the sibling DK-AC-MBS-1 — which connects to the indoor PCB connector of residential Daikin RAC units — the DK-RC-MBS-1 attaches to the Daikin P1P2 wired remote-controller bus, the same two-wire bus used by the optional Daikin BRC controller. This makes it the right choice for commercial VRV (heat pump and heat recovery) and SKY Air installations.

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, vane position control, thermostat with setpoint and current temperature, and error code monitoring. A single gateway can drive up to 16 indoor units as one logical unit, and up to 63 gateways can share a single EIA-485 bus.

Hardware connection#

The gateway has two pluggable terminal blocks:

• P1P2 bus (2-pole green plug-in terminal: P1 / P2) — connects to the Daikin remote-controller bus. The same bus that wires a Daikin BRC controller to the indoor unit. The P1P2 connection has no specific polarity — P1 and P2 are interchangeable.
• EIA-485 bus (2-pole green plug-in terminal: A+ / B-) — connects to the Modbus RTU bus where TapHome’s TCP-to-RTU bridge sits as Modbus master. Observe polarity on this side.

The gateway is powered directly from the Daikin AC indoor unit via the P1P2 bus — no external power supply is needed. The AC indoor unit must therefore be connected to mains for the gateway to communicate.

Wiring diagram

There are two valid topologies on the P1P2 bus, selected by DIP switch SW1-P1..P2:

• Daikin BRC wired controller present — connect the gateway in parallel with the existing Daikin BRC at any point on the P1P2 line. The BRC stays as Master, the gateway is configured as Slave (SW1-P1..P2 = default). Both the BRC and the Modbus side can issue commands simultaneously.
• No wired controller — connect the gateway directly to the indoor unit’s P1P2 bus and configure it as Master. Only the gateway controls the AC.

Disconnect the AC unit from mains power before opening the indoor unit. Only one device on the P1P2 bus can be Master — if both the Daikin BRC and the gateway are configured as Master, communication will shut down. Keep the P1P2 communication cable away from electrical wires and ground wires; do not bundle them together. Maximum P1P2 bus length is 500 m / 1,640 ft, EIA-485 bus length is 1,200 m / 3,937 ft (max 32 devices per RS-485 segment).

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 sits at one end of the bus. Loop and star topologies are not allowed on EIA-485. A fail-safe biasing mechanism is required and must be supplied by the Modbus master (typically built into the TCP-to-RTU bridge).

Enabling Modbus communication#

The gateway has three DIP switch banks on the front face: SW1 (4 pins — Master/Slave + VRV operation mode + temperature sensor source), SW3 (8 pins — slave address + baud rate), SW4 (4 pins — temperature scale + EIA-485 termination). All defaults are usable out of the box, so on a typical installation only the slave address and EIA-485 termination need to be reviewed. Every DIP switch change requires a power cycle to take effect.

SW1 — Master/Slave, VRV operation mode and temperature reading source

The Master/Slave of Operation Mode setting (SW1-P3) only applies to VRV heat-pump systems with multiple indoor units running different modes. The heat-pump outdoor unit can only operate in one mode at a time — the indoor unit configured as Master defines that mode, the rest follow as Slaves and are restricted to the modes shown in Appendix A of the user manual (e.g. when Master = Cool, Slaves can only run Cool, Fan or Dry).

SW3 — Modbus slave address (P1..P6) and baud rate (P7..P8)

The slave address is binary-encoded across SW3-P1..P6 with P1 = LSB. Range: 0..63. Common examples:

Baud rate is selected by SW3-P7, SW3-P8 and SW4-P3 combined:

Default frame format is 8N2 (8 data bits, no parity, 2 stop bits). 8N1 is also auto-detected — no manual setting needed. The gateway implements Modbus functions 03, 04, 06 and 16, with a polling limit of 50 registers per single read and 1 register per single write (function 16 must always carry length = 1).

SW4 — Temperature scale, baud rate bit and EIA-485 termination

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 DK-RC-MBS-1 gateways on a single bus — each can drive up to 16 Daikin indoor units controlled as one logical group.

Device capabilities#

The template exposes 6 devices polled from holding registers H:0 through H:11.

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 Daikin:

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 Daikin VRV/SKY Air units. Reads and writes register H:1 (Int16). Poll interval: 2.5 s.

Fan Speed

Fan speed selector. Over the Daikin P1P2 bus only Auto, Low, Mid, High are documented:

The TapHome template adds an extra Quiet position at value 1, shifting Low to 2, Mid to 3 and High to 4. The Daikin user manual does not document a Quiet speed on the P1P2 bus — selecting “Quiet” in TapHome will actually issue the Daikin command for Low, “Low” will issue Mid, and so on. Register H:21 (read-only, not exposed in the template) reports the maximum number of fan speeds the connected indoor unit actually supports — the UI may expose more positions than the unit accepts.

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 Daikin manual reserves register value 10 for Swing and uses a sparse value set (1..5, 10). The TapHome template remaps Swing onto value 5 to keep the multi-value switch range contiguous, and swaps Position 4 and Position 5 in the value mapping: template slot 4 is labelled “Position 5 (Vertical)” but the underlying Daikin command corresponds to register value 4 (Position 4); slot 6 is labelled “Position 4 (Vertical)” but issues register value 6, which is not documented for Daikin. Until the template is corrected, expect the labels for Position 4 and Position 5 to behave inverted on real Daikin units.

Horizontal (L/R) vane position is documented separately on register H:26 (Auto / Swing) but is not exposed by the current template. 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 Daikin units is 16–31 °C (61–88 °F). The reference temperature shows the AC unit’s own sensor reading (or 0x8000 / -32768 when no value has yet been received from the indoor unit).

The TapHome template applies a /100 divisor to the temperature registers, but the DK-RC-MBS-1 user manual only documents three temperature modes selectable via SW4-P1 / SW4-P2: x1 Celsius (default), x10 decicelsius and Fahrenheit (x1). There is no documented x100 (centi-degree) mode for this gateway. On a default-configured Celsius unit setpoints can therefore appear 100× too small (e.g. 0.22 °C instead of 22 °C). If you observe such scaling, 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:

The full Daikin error-code table is published in section 9 of the user manual and is shared across VRV and SKY Air systems. It covers indoor unit faults (A0–CF), outdoor unit faults (E0–LC, P0–PJ), system faults (U0–UF), centralised-control faults (M2–MC) and others. When more than one indoor unit shares a single gateway, register H:81 (read-only, not exposed in the template) reports the indoor unit number that triggered the error.

Poll interval: 15 s.

Troubleshooting#

No Modbus communication

1. Verify the AC indoor unit is powered on — the gateway is powered via the P1P2 bus and will not respond at all until the indoor unit’s mains is connected.
2. Check the LED indicators: LED1 + LED2 pulse (3 s ON) at startup; LED1 flashing (100 ms ON / 1900 ms OFF) indicates normal operation; LED1 blinking (500 ms ON / 500 ms OFF) indicates a communication error with the AC unit; LED2 pulse (3 s) indicates an under-voltage event on the P1P2 bus.
3. Confirm the slave address in TapHome matches the SW3-P1..P6 binary setting on the gateway (each pin = one bit, P1 = LSB).
4. Ensure the TCP-to-RTU bridge is on the same network as TapHome Core and the bridge’s serial settings match SW3 + SW4-P3 baud rate (default 9600 bps, 8N2).
5. Verify the EIA-485 polarity — A+ / B- must be consistent across all devices on the bus.
6. 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 Daikin AC indoor unit over the P1P2 bus. Check:

• P1P2 cable is connected at both ends (no specific polarity, but both wires must be present).
• The AC indoor unit is powered (mains).
• If a Daikin BRC wired controller is also present, confirm only one device (gateway or BRC) is configured as Master — verify SW1-P1..P2 against the topology.
• P1P2 bus length does not exceed 500 m.
• LED2 is not pulsing under-voltage — if it is, check the indoor unit’s auxiliary supply on the P1P2 line.

Master/Slave conflict on the P1P2 bus

If the Daikin BRC and the gateway are both configured as Master, the P1P2 bus will collide and one or both devices will stop responding. Set SW1-P1..P2 to Slave (default) whenever a BRC is present on the same bus and is configured as Master, and to Master only when no Daikin wired controller is connected (or when the BRC is itself set to Slave).

Temperature values are incorrect

The template uses a /100 divisor on registers H:4 and H:5. The default DIP setting (SW4-P1 = OFF, SW4-P2 = OFF) sends temperature in integer degrees Celsius (x1) — with /100 scaling on the TapHome side, a setpoint of 22 °C will be reported as 0.22 °C. Use the Modbus debug tool in TapHome to read raw register values and compare with the expected setpoint, then either reconfigure the gateway or adjust the divisor in the template scripts.

Vane Position 4 / Position 5 behave swapped

The TapHome template swaps the Daikin Position 4 (Vertical) and Position 5 (Vertical) labels in the multi-value switch. If the louver moves to a different angle than the label suggests, this is the cause — selecting “Position 5 (Vertical)” actually sends the Daikin command for Position 4, and vice versa. Choose the slot that produces the desired physical louver position rather than relying on the label until the template is corrected.

Local remote controller cannot change setpoint (virtual temperature active)

The DK-RC-MBS-1 supports an “external ambient temperature” feature (register H:22, not exposed in the current template) that activates a Daikin virtual-temperature mechanism: SAC = TAC − (TBMS − SBMS). While active, the Daikin BRC cannot change the setpoint because the indoor unit’s setpoint is exclusively driven by the virtual-temperature correction. To deactivate it from the Modbus side, write -32768 (0x8000) to register H:22 — this clears the external reference and returns setpoint control to the BRC.

DIP switch changes have no effect

DIP-switch configuration only takes effect after a power cycle of the gateway. Disconnect the AC indoor unit from mains for at least 10 seconds, then reconnect it — the gateway is powered from the P1P2 bus and will pick up the new DIP settings on boot.