The IntesisBOX MH-RC-MBS-1 (current order code INMBSMHI001R000) is a Modbus gateway by Intesis (HMS Networks) that interfaces Mitsubishi Heavy Industries FD (commercial / ducted) and VRF (KX6) air conditioning systems with Modbus RTU (EIA-485) networks. A single gateway can manage up to 16 MHI indoor units connected to the same XY bus, controlled as one group.
TapHome connects to the gateway via Modbus TCP using a TCP-to-RTU bridge — the gateway itself communicates with the MHI AC system over the proprietary XY bus. The template provides ON/OFF control, operating mode selection, fan speed adjustment, vane position control, and thermostat with setpoint and current reference temperature.
Hardware connection
The gateway has two plug-in terminal blocks:
- XY bus (2 poles, no polarity) — connects to the Mitsubishi Heavy Industries XY bus of the indoor unit
- EIA-485 connector (2 poles, A+ / B-) — connects to the Modbus RTU bus
The gateway is powered directly from the MHI XY bus — no external power supply is needed. Mounting options include DIN rail (EN60715 TH35), wall mount, or inside the AC indoor unit.
Disconnect the AC unit from mains power before opening the indoor unit and connecting the gateway. If an MHI wired remote controller is connected to the same XY bus, the gateway and the remote controller must be configured as a Master/Slave pair (see below) — otherwise XY bus communication may shut down.
Connection scenarios
The MH-RC-MBS-1 can operate in two roles on the MHI XY bus, selectable via DIP switch SW1-P1:
- Gateway as Slave (SW1-P1 OFF, default) — a genuine MHI wired remote controller must be present on the XY bus and configured as Master. The gateway reads and writes in parallel with the remote controller.
- Gateway as Master (SW1-P1 ON) — no MHI wired remote controller is present (or if one exists, it must be configured as Slave). The gateway drives the XY bus directly.
Constraints:
- Maximum XY bus length: 600 m / 1,968 ft
- Maximum EIA-485 bus length: 1,200 m / 3,937 ft
- EIA-485 loop or star topologies are not allowed
- A 120 Ω termination resistor is required at each end of the EIA-485 bus (one can be provided by the gateway — see SW4-P4 below)
Configuration
All settings are controlled via three on-board DIP switches: SW1 (AC indoor unit features), SW3 (Modbus slave address and baud rate), and SW4 (baud rate, temperature format, and EIA-485 termination).
The gateway must be power-cycled every time a DIP switch is changed for the new configuration to take effect.
Installation steps
- Disconnect the AC indoor unit from mains power.
- Wire the XY bus between the gateway and the indoor unit (two-wire, no polarity).
- Wire the EIA-485 bus to the gateway (A+, B-), respecting polarity and topology (no loop / no star).
- Set the DIP switches as described below — defaults work for most installations.
- Reconnect the AC indoor unit to mains power and power-cycle the gateway.
Required DIP switch settings
The gateway ships with defaults that work with the TapHome template. Most installations only need to verify that the slave address and baud rate match the TapHome side.
Critical for template compatibility — leave at default:
- SW4-P1 OFF (x1 degrees) — the template reads temperature registers as raw Int16 with no scaling. If set to ON (x10), a 22 °C setpoint would appear as 220 °C.
- SW4-P2 OFF (Celsius) — the template’s setpoint ranges (16–30 °C) assume Celsius encoding.
- SW1-P4 ON (vanes enabled) — required for the Vane Position device to function. Leave OFF only if the indoor unit has no louvers.
Must match the TapHome side:
- SW3-P1..P6 — Modbus slave address (binary-encoded, 1..63). Default: 1 (P1 ON, rest OFF). Must match the
Slave IDimport parameter. Register H:15 reports the currently configured address. - SW3-P7..P8 + SW4-P3 — baud rate. Default: 9600 bps. Must match the Modbus RTU↔TCP bridge configuration. Supported rates: 2400, 4800, 9600, 19200, 38400, 57600, 76800, 115200. Register H:14 reports the currently configured rate.
Adjust only when needed:
- SW1-P1 (default OFF = Slave) — change to ON (Master) only if no MHI wired remote controller is present on the XY bus.
- SW1-P2..P3 (default = 4) — fan-speed count supported by the indoor unit. The template exposes 5 values (Auto + 4 speeds); if set to fewer, the higher speeds will be rejected by the unit. Register H:21 reports the configured fan-speed count.
- SW4-P4 (default OFF) — enable the internal 120 Ω EIA-485 termination resistor only if the gateway is at one end of the bus.
For the full 0..63 slave-address binary table and all baud-rate switch combinations, refer to the installation sheet PDF linked above.
TapHome connection
Since the gateway is physically Modbus RTU on EIA-485, a Modbus TCP-to-RTU bridge (for example Waveshare or USR-IOT) 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 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-P1..P6 (default: 1)
Assign a static IP address to the TCP-to-RTU bridge in the router’s DHCP settings so that it does not change after a power cycle.
Device capabilities
The template exposes 5 devices communicating over holding registers H:0 through H:5. A single template instance controls one AC group (up to 16 MHI indoor units connected to the same XY bus behave as one unit).
ON/OFF
Simple switch to turn the AC group on or off. Reads and writes register H:0 (Bool): 0 = Off, 1 = On.
Mode
Operating mode selector with 5 modes documented by Intesis:
| Value | Mode |
|---|---|
| 0 | Auto |
| 1 | Heat |
| 2 | Dry |
| 3 | Fan |
| 4 | Cool |
Reads and writes register H:1 (Int16). The template defines 10 positions (values 0–9); values 5–9 are placeholder slots and should not be used.
Fan Speed
Fan speed selector. The MHI AC family supports up to 5 positions:
| Value | Speed |
|---|---|
| 0 | Auto |
| 1 | Low |
| 2 | Mid |
| 3 | High |
| 4 | Powerful |
Reads and writes register H:2 (Int16). The actual number of available fan speeds depends on the indoor unit and on the SW1-P2..P3 DIP switch configuration (1, 2, 3, or 4 speeds). Register H:21 reports the maximum configured fan-speed count.
Vane Position
Vane position control. The user manual documents positions 1–4 and Swing (register value 10). The template remaps these into a contiguous range for the multi-value switch:
| Value (template) | Position |
|---|---|
| 0 | Position 1 |
| 1 | Position 2 |
| 2 | Position 3 |
| 3 | Position 4 |
| 4 | Swing |
Reads and writes register H:3 (Int16). The vane feature must be enabled via SW1-P4 (default ON). If the indoor unit does not support vanes, set SW1-P4 OFF.
Thermostat
Temperature setpoint (register H:4, read/write) and current reference temperature (register H:5, read-only). The template uses raw Int16 values in °C with no scaling — SW4-P1 must stay OFF (x1 mode) and SW4-P2 OFF (Celsius).
MHI setpoint ranges:
- All modes except heat: 18..30 °C
- Heat: 16..30 °C
Reference temperature range: 10..38 °C. The reference shows the AC unit’s own sensor reading unless an external sensor value has been written to register H:22 (not exposed by the template, see the Virtual Temperature mechanism in the user manual).
Troubleshooting
No Modbus communication
- Verify the MHI indoor unit is powered on — the gateway is powered from the XY bus.
- Check the LED indicators: L1 + L2 pulse (5 s ON) indicates 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 pulse (3 s ON) indicates under-voltage.
- Confirm the slave ID set in TapHome matches the SW3-P1..P6 DIP switch configuration on the gateway.
- Confirm the baud rate configured on the TCP-to-RTU bridge matches SW3-P7..P8 + SW4-P3 (default 9600 bps, 8N2).
- Verify that the TCP-to-RTU bridge is reachable from TapHome Core (same local network, correct IP address).
- Check EIA-485 polarity: A+ / B- must be consistent across all devices on the bus.
- Power-cycle the gateway after any DIP switch change.
Gateway does not start — L2 red LED pulsing
A 3 s pulse on the L2 red LED indicates under-voltage. Verify that the MHI indoor unit is fully powered and that the XY bus wiring is correctly connected (X and Y terminals of both devices). The gateway draws its supply from the XY bus.
Error code 65532 after power-up
When the gateway is configured as Master of the XY bus (SW1-P1 ON), it performs an initialization sequence of approximately 2 minutes before normal operation starts. Register H:11 (Error Code, not in the template) reports 65532 during this phase. Wait for the sequence to complete.
Error code 65535 continuously
This indicates the gateway cannot communicate with the MHI AC system over the XY bus. Check the XY wiring and terminal screws. If the AC has a wired MHI remote controller, verify that exactly one device on the XY bus is configured as Master (either the remote controller or the gateway, not both).
Temperature values are incorrect
The TapHome template uses raw Int16 values. Keep SW4-P1 OFF (x1 degrees) and SW4-P2 OFF (Celsius). If SW4-P1 is ON (x10 / decidegrees), a setpoint of 22 °C is transmitted as 220, which the template would display as 220 °C. Use the Modbus debug tool in TapHome to read the raw value of register H:4 and confirm the scale.
AC unit ignores setpoint changes
Check register H:46 (Center / Remote, not in the template — readable via Modbus debug). Values 1 (Remote lock On/Off — Center) and 2 (Remote lock All — Center) restrict remote-controller writes, value 3 (Remote Only) disables BMS writes entirely. The default is 0 (Unlock). See user manual section 4.2.4.
