The Sinclair Uni Split is a DC Inverter split air conditioning unit with an integrated Modbus RTU (RS-485) BMS interface built directly into the indoor unit controller. No external communication module is required. The TapHome template provides temperature control, operation mode selection, fan speed, vertical and horizontal swing positions, sleep mode and outdoor temperature monitoring.
Up to 255 units can be connected on a single Modbus RTU bus. Each unit requires a unique slave address (1–255) configured through the wired controller (refer to the unit’s service manual for the address setting procedure).
Hardware connection
RS-485 wiring
The Sinclair Uni Split indoor unit has an integrated RS-485 interface that connects directly to TapHome Core:
- A+ on the indoor unit RS-485 terminal –> A+/D+ on TapHome
- B- on the indoor unit RS-485 terminal –> B-/D- on TapHome
- GND –> GND on TapHome power supply
Important – Grounding
The GND wire must be connected between the indoor unit and TapHome. Without proper grounding, communication errors may occur.
Technical specifications
| Parameter | Value |
|---|---|
| Interface | RS-485 |
| Protocol | Modbus RTU |
| Baud rate | 9600 bps (default) |
| Data bits | 8 |
| Parity | None |
| Stop bits | 1 |
| Slave address | 1–255 |
| Max units | 255 per bus |
Configuration
Enabling Modbus communication
The Modbus interface is integrated into the indoor unit controller and is active by default. The slave address must be configured through the wired controller before connecting to TapHome:
- Access the service settings on the wired controller (refer to the unit’s service manual)
- Set the Modbus slave address (1–255). Use address 1 for a single unit
- Set the address mode: “central controller” mode supports addresses 1–16; “PC address” mode supports addresses 1–255
- Connect the RS-485 wiring between the unit and TapHome Core
- In TapHome, configure the Modbus RTU connection with: 9600 baud, no parity, 1 stop bit, 8 data bits
The BMS/PC control is equal to the local control. The command sent later takes priority – if TapHome writes a value, it can be overridden by the local remote controller and vice versa.
Device capabilities
Temperature control
Ambient Temperature (H:4 read / H:20 write) is the primary thermostat device. It reads the indoor ambient temperature from register H:4 with x10 encoding (divided by 10 for display in degrees Celsius) and writes the temperature setpoint to register H:20 in the range of 16–30 degrees Celsius.
Two service attributes provide additional temperature readings:
- Temperature of Air Return (H:82) – ambient temperature at the air return port (x10 encoding)
- Temperature of Light Board (H:83) – ambient temperature of the indoor unit’s light board (x10 encoding)
Outdoor Temperature (H:49) reads the outdoor ambient temperature directly in degrees Celsius (no conversion needed, accuracy 1 degree Celsius, range -100 to 155 degrees Celsius).
Power and operation mode
- Power ON/OFF (H:2) – turns the indoor unit on (0xAA = 170) or off (0x55 = 85). The template uses a Switch() conversion to map these values to standard ON/OFF states
- Operation Mode (H:17) – selects the operating mode: Cooling (1), Heating (2), Drying (3), Fan Only (4), or Auto (5)
Cooling-only units: On units that support cooling only, the heating mode command is invalid. The unit will not respond to heating instructions.
Fan speed
Fan Speed (H:19) controls the fan with seven levels: Auto (0), Very Low (1), Low (2), Medium (3), High (4), Very High (5), and Turbo (6).
Swing control
Up/Down Swing (H:22) controls the vertical vane position with 10 options: Off (0), Full Swing (1), Position 1–5 (2–6), 3-5 Area Swing (7), 2-5 Area Swing (8), and 2-4 Area Swing (9).
Left/Right Swing (H:23) controls the horizontal vane position: Off (0), Same Direction Swing (1), Position 1–5 (2–6), Opposite Direction Swing (7), and 1-5 Position (9).
Sleep mode
Sleep Mode (H:25) provides four options: No Sleep (0), Sleep Mode 1 (1), Sleep Mode 2 (2), and Sleep Mode 3 (3). Each sleep mode applies different temperature adjustments during the night for improved comfort and energy savings.
Sleep mode is invalid when the unit is in Fan Only or Auto mode.
Additional capabilities
The Sinclair Uni Split also exposes Modbus registers for fresh air valve control, clean function with contamination grade monitoring, energy saving temperature limits (cooling lower limit and heating upper limit), remote lock and shield functions (temperature, mode, ON/OFF, energy saving), absence mode (sets temperature to 8 degrees Celsius), turbo mode, silent mode, X-fan (post-shutdown fan operation), child lock, and Celsius/Fahrenheit selection. Read-only status registers include compressor status, outdoor fan status, 4-way valve status, system defrosting state, and cooling-only/heat-pump identification. These can be added in a future template update.
The energy saving registers (H:35, H:36) allow setting temperature limits for cooling and heating. When energy saving is active, the setpoint must respect these limits – otherwise the unit will not respond to temperature commands.
Troubleshooting
No Modbus communication
- Check RS-485 cables: Verify A+, B-, and GND connections between the indoor unit and TapHome Core
- Verify the slave address: Confirm the address set on the wired controller matches the TapHome configuration
- Check communication parameters: TapHome must be set to 9600 baud, no parity, 1 stop bit, 8 data bits
- Power cycle the unit: After the indoor unit powers on, it may report alarm code 0x04 until it receives the first valid Modbus frame – this is normal behavior
Alarm code 0x04 (slave device failure)
This alarm indicates communication failure between the Modbus interface and the air conditioning unit itself. Check:
- The indoor unit is powered on and operating normally
- The wired controller is properly connected
- Power cycle the indoor unit if the error persists
Alarm code 0x03 (illegal data)
The transmitted data is incorrect or beyond the valid range. Verify that register values being written are within the documented ranges (e.g., temperature setpoint 16–30, fan speed 0–6, mode 1–5).
Heating mode not working
Check whether the unit is a cooling-only model. Read Coil bit 177 – if the value is 1, the unit supports cooling only, and heating commands are invalid.
