The IntesisBOX HI-RC-MBS-1 (order code INMBSHIT001R000, legacy HI-RC-MBS-1) is a Modbus gateway by Intesis (HMS Networks) that interfaces Hitachi air conditioners — the commercial line for air conditioners commercialized by Hitachi, including VRF indoor units sharing the Hitachi AB control protocol — with Modbus RTU (EIA-485) networks. The gateway attaches to the Hitachi AB bus — the same 2-wire bus used by the wired Hitachi remote controller — and a single gateway can address up to 16 Hitachi indoor units controlled as one group (group control, not individual addressing).
TapHome connects to the gateway via Modbus TCP through a TCP-to-RTU bridge — the gateway itself is a native Modbus RTU slave with no built-in Ethernet. 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 Hitachi indoor units can be verified using the Intesis HVAC Compatibility Tool.
INMBSHIT001R000 is a legacy product, replaced by IN485HIT001R000 in the current HMS Networks catalogue. The successor part has the same enclosure and wiring but provides native Modbus TCP/RTU — it would not require an external TCP-to-RTU bridge between the IntesisBOX and TapHome Core. Existing R000 deployments remain functional.
Hardware connection
The gateway has two plug-in 2-pole screw terminal blocks:
- AB bus (2 poles — terminals A, B) — connects to the Hitachi AB bus on the indoor unit’s remote-controller terminals, in parallel with any Hitachi 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 Hitachi AB bus — 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 HI-RC-MBS-1 gateways can share the same Modbus RTU EIA-485 bus, each addressed via SW3-P1..P6. Each gateway connects to up to 16 Hitachi indoor units on its own AB bus, which the gateway treats as one group (not individually addressable from Modbus). TapHome (acting as Modbus master through a TCP-to-RTU bridge) sees every gateway as a separate Modbus slave. Modbus repeaters may be required on long EIA-485 lines or at higher baud rates.
AB-bus wiring
The AB bus is a 2-wire bus with no polarity sensitivity — terminals A and B can be connected without minding wire order. Two installation scenarios are supported:
- Wired remote controller available — connect the gateway as Slave (SW1-P1 = OFF) in parallel with the Hitachi wired remote controller, which acts as Master. Both share the AB bus.
- No wired remote controller available — connect the gateway as Master (SW1-P1 = ON) directly to the AB bus. If a controller is added later, it must be configured as Slave.
Maximum AB bus length is 500 m / 1,640 ft. Any 2-wire cable can be used (the cable is not supplied with the gateway). 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. If more than one AC unit is connected to the same AB bus, a Hitachi wired remote controller (set as Master of the bus) is required — the gateway alone cannot drive a multi-IDU AB bus. Keep the AB 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 HI-RC-MBS-1 is configurable via on-board DIP switches and via Modbus registers. Default settings (slave address 1, 9600 bps 8N2, all other DIP switches OFF) work out of the box on a typical single-IDU installation, so usually only the slave address, the gateway role on the AB bus (SW1-P1) 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 AB bus loses its supply, then reconnecting after a few seconds.
DIP-switch layout
The gateway has three DIP-switch banks: SW1 (4 positions, AB-bus role), SW3 (8 positions, Modbus slave address + baud rate) and SW4 (4 positions, temperature format + EIA-485 termination).
Enabling Modbus communication
The HI-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. The gateway implements Modbus functions 3 (Read Holding Registers), 4 (Read Input Registers), 6 (Write Single Register) and 16 (Write Multiple Registers — limited to 1 register per request).
SW1 — AB-bus role
| Position | Default (OFF) | ON |
|---|---|---|
| SW1-P1 | Slave — gateway is AB-bus Slave; a Hitachi wired remote controller must be present, configured as Master. | Master — gateway is AB-bus Master; no Hitachi wired controller present, or if present it must be Slave. |
| SW1-P2 | Not used. | Not used. |
| SW1-P3 | Not used. | Not used. |
| SW1-P4 | Not used. | Not used. |
The Master/Slave state is also exposed read/write on Modbus register H:98 (0 = Slave, 1 = Master) — 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. If more than one AC indoor unit is connected to the same AB bus, the gateway must be Slave and a Hitachi wired remote controller must be present as Master of the bus.
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 (address 0 is reserved as Modbus broadcast). 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. |
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 HI-RC-MBS-1 gateways on a single bus — useful when each gateway controls a different group of Hitachi indoor units. The successor product IN485HIT001R000 has native Modbus TCP and would not require a bridge — consider it for new installations.
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. The gateway and the Hitachi wired remote controllers can be used simultaneously — Modbus commands and the AC’s own remote both act on the indoor unit, and both stay synchronised regardless of which side issues the command. Reads and writes register H:0 (Bool). Poll interval: 2.5 s.
Mode
Operating mode selector with the 5 modes documented by Hitachi:
| 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 Hitachi indoor units. The actual modes available also depend on the AC unit’s capabilities — some Hitachi commercial IDUs may not support all five modes. Reads and writes register H:1 (Int16). Poll interval: 2.5 s.
Fan Speed
Fan speed selector. The Hitachi user manual documents the following encoding on the AB bus:
| Manual value | Speed |
|---|---|
| 0 | Auto |
| 1 | Low |
| 2 | Mid |
| 3 | High |
| 4 | Super-high |
The TapHome template reorders the fan-speed labels relative to the Hitachi register encoding and inserts an undocumented “Mid-1” slot:
- Slot 2 “Mid-1” writes register value 2 — the Hitachi manual has a single “Mid” speed at value 2 (no “Mid-1” exists for Hitachi). The “Mid-1” label is borrowed from sibling Intesis RC gateways and duplicates “Mid” under a different label.
- Slot 3 “Mid” writes register value 3 → on a real Hitachi unit this is High, not Mid.
- Slot 4 “Super-High” writes register value 4 → matches Super-high (correct).
- Slot 5 “High” writes register value 5 → undocumented per the Hitachi manual (real units only define 0–4 for fan speed).
Effectively only Auto, Low and Super-High are correctly labelled. Verify the actual fan-speed mapping at commissioning. Register H:21 (read-only, not exposed in the template) reports the actual maximum number of supported fan speeds for the connected Hitachi indoor unit — useful to know how many slots are physically reachable.
Reads and writes register H:2 (Int16). Poll interval: 2.5 s.
Vane Position
Vertical (U/D) vane position control. The Hitachi user manual documents the following encoding:
| Manual value | Position |
|---|---|
| 1 | POS1 (Horizontal) |
| 2 | POS2 (Horizontal) |
| 3 | POS3 (Medium) |
| 4 | POS4 (Vertical) |
| 5 | POS5 (Vertical) |
| 6 | POS6 |
| 7 | POS7 |
| 10 | Swing |
The TapHome template remaps Hitachi’s sparse value set (1–7 + 10) onto the contiguous MultiValueSwitch range 0–9, with several mismatches versus the manual:
- Slot 4 “Position-5 (Vertical)” writes register value 4 — but the manual defines value 4 as POS4 (Vertical). Selecting “Position-5” sends the IDU to POS4, not POS5.
- Slot 5 “Swing” writes register value 5 — but the manual reserves value 5 for POS5 (Vertical) and the documented Swing value is 10. Selecting “Swing” in TapHome will set the vane to POS5 (Vertical) on a real Hitachi unit, not Swing — the documented Swing value (10) is unreachable through the current MultiValueSwitch encoding.
- Slot 6 “Position-4 (Vertical)” writes register value 6 — but the manual defines value 6 as POS6, not POS4.
- Slots 7–9 (“7”, “8”, “9”) write register values 7–9. Only POS7 (value 7) is documented for Hitachi vanes; values 8–9 are undocumented.
- Slot 0 (“0”) is also undocumented — the Hitachi manual starts the vane range at value 1.
Effectively only POS1 (slot 1), POS2 (slot 2) and POS3 (slot 3) are correctly labelled. Verify the actual physical vane positions at commissioning rather than relying on the labels. Available positions also depend on the connected Hitachi indoor unit’s capabilities — refer to the Intesis IDU compatibility matrix.
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). Valid ranges per the Hitachi user manual:
- Setpoint: 16–32 °C (61–94 °F)
- Reference temperature: manufacturer-specific range (see Hitachi IDU manual)
Both registers report −32768 (0x8000) at startup until the gateway has read a value from the indoor unit. The reference temperature reflects the indoor unit’s own control-loop sensor — either the return-path thermistor or the wired remote controller’s thermistor, depending on the IDU configuration.
The TapHome template applies a /100 divisor to the temperature registers, but the HI-RC-MBS-1 user manual only documents three temperature modes selectable via SW4-P1 / SW4-P2: ×1 Celsius (default), ×10 decicelsius and Fahrenheit (×1). There is no documented ×100 (centi-degree) mode for this gateway. On a default-configured Celsius unit, setpoints can therefore appear 100× too small (e.g.
0.22 °Cinstead of22 °C); on a ×10 decicelsius configuration they will be 10× too small. 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.
Poll interval: 2.5 s.
Error Code
Read-only numeric value from register H:11. Key values:
| Value | Meaning |
|---|---|
| 0 | No active error |
| 65535 (−1 signed) | Communication error between the Intesis gateway (or remote controller) and the AC unit |
| Other | Hitachi fault code — see categories below |
The full error-code table is published in section 7 of the user manual and the Modbus error code matches the value displayed by the Hitachi wired remote controller. Hitachi uses two error-code formats — a decimal value on Modbus / decimal displays and a controller-specific alphanumeric format (e.g. decimal 17 corresponds to controller code 11). Selected categories:
| Range | Category examples |
|---|---|
| 01–09 | Indoor / outdoor unit protection device tripping; transmission abnormality between IDU and ODU; inverter ↔ control PCB; power-source wiring; voltage drop; AC input over-current; expansion-valve drive error; outdoor-unit heater overheat |
| 17–25 | Indoor-unit sensor faults — dust collector / no-maintenance filter, capacity setting, water-supply shortage, humidifier leaking, sensor system malfunctions |
| 33–57 | Outdoor-unit sensor faults — drain water sensor, heat-exchanger liquid/gas-pipe thermistors, fan-motor sensor, swing-flap motor sensor, AC input over-current sensor, suction/discharge air thermistors, contamination, humidity, remote-control thermistor, radiation sensor |
| 67–71 | Pressure faults — high-pressure switch sensor, protection devices activated, outdoor PCB assembly failure, HPS / LPS activated |
| 81–88 | Inverter faults — overload / over-current of inverter or STD compressor motor, fan-motor over-current, AC input over-current, expansion-valve drive error, four-way valve error, pump-motor over-current |
| 176–181, 238 | IU model / number setting and address errors; H-LINK setting errors; water-temperature abnormal |
| 65535 | Gateway↔AC communication failure (signed −1) |
The Modbus error code matches the value shown on the Hitachi wired remote controller’s display — useful for cross-checking faults from the TapHome side without physical access to the controller. The companion register H:10 (Alarm Status, read-only, not exposed in the template) is a 0/1 boolean — useful for triggering automation rules without parsing the full error-code table. The error-reset action H:45 (write 1) and the per-IDU error-address register H:81 (which IDU number reported the fault, relevant for multi-IDU groups) are also documented but not exposed in the current template.
Poll interval: 15 s (vs 2.5 s for the control registers).
Troubleshooting
No Modbus communication
- Verify the Hitachi indoor unit is powered on — the gateway is bus-powered from the AB bus and will not respond at all until the indoor unit’s mains is connected.
- Check the on-board LED indicators:
- L1 + L2 pulse together (5 s ON) on power-up — device reset / start-up sequence.
- L1 flashing 100 ms ON / 1900 ms OFF — gateway correctly configured and working.
- L1 blinking 500 ms ON / 500 ms OFF — communication error between the gateway and the AC unit on the AB bus.
- L2 pulsing 3 s ON — under-voltage on the AB bus (verify IDU mains).
- L1 / L2 alternating blink 500 ms / 500 ms — flash checksum failure (firmware corruption — replace the gateway).
- Confirm the slave address in TapHome matches the SW3-P1..P6 binary setting on the gateway (each pin = one bit, P1 = LSB).
- 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 — 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 Hitachi AC indoor unit over the AB bus. Check:
- The A and B wires are connected at both ends of the bus (the bus has no polarity sensitivity, but both wires must be present and continuous).
- The Hitachi indoor unit is powered (mains).
- The L1 LED is blinking 500 ms / 500 ms — confirming an AB-bus-side communication error.
- AB bus length does not exceed 500 m.
- If a Hitachi wired remote controller is also present, confirm only one device (gateway or controller) is configured as Master — verify SW1-P1 against the topology.
- For multi-IDU groups (more than one indoor unit on the same AB bus), a Hitachi wired remote controller must be present and configured as Master — the gateway alone cannot drive a multi-IDU bus.
Master/Slave conflict on the AB bus
If the Hitachi wired remote controller and the gateway are both configured as Master, the AB bus will collide and one or both devices will stop responding. Set SW1-P1 to OFF (gateway as Slave) whenever a Hitachi wired controller is present on the same bus, and to ON (gateway as Master) only when no Hitachi 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 HI-RC-MBS-1 supports three temperature representations on the AB side — ×1 Celsius (SW4-P1 OFF, SW4-P2 OFF — default), ×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 on a default Celsius unit, 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 Hitachi 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). While the Virtual Temperature mechanism is active:
- The Hitachi remote controller may display a different number than the user-requested setpoint (register H:4).
- Register H:23 (AC Real temperature setpoint, read-only, not exposed in the template) reports the value actually applied to the indoor unit.
- To use the wired remote controller’s reading as the external reference, the controller must be configured as Master and the option “thermostat sensor in the Remote Controller” must be activated by a Hitachi-authorized installer.
- When the gateway is configured as Master of the AB bus, the external temperature is applied directly to the IDU (no Virtual Temperature) and the Hitachi remote controller cannot send the external reference value.
To deactivate the Virtual Temperature mechanism from the Modbus side, write −32768 (0x8000) to register H:22 — this clears the external reference and returns control to the IDU’s own return-path / remote-controller sensor.
Fan Speed and Vane Position labels are wrong
The TapHome template’s MultiValueSwitch label-to-value mapping does not fully match the Hitachi register encoding (see the warnings under “Fan Speed” and “Vane Position” above). Until the template is corrected, choose the slot that produces the desired physical behaviour rather than relying on the label — and document the working mapping in the project notes after commissioning.
DIP-switch change has no 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 supply on the AB bus) and reconnecting after a few seconds. Modifying DIP switches while the gateway is powered will not change the active configuration.
