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Fujitsu Air Condition via UTY-VMSX

Modbus RTU
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Last updated: 03. 2026

Requires external gateway

Fujitsu UTY-VMSX

Fujitsu Air Condition via UTY-VMSX

The Fujitsu UTY-VMSX is a Modbus RTU converter that connects a single Fujitsu indoor AC unit to TapHome via RS-485. The converter acts as a Modbus slave, exposing temperature control, operation modes, fan speed, vertical and horizontal airflow direction, energy save mode, anti-freeze protection and human detection auto off functions.

Each UTY-VMSX controls one indoor unit. Up to 31 converters can be connected on a single Modbus bus (247 with a repeater). The slave address is configured via DIP switches (SET4/SET5) on the PCB.

Hardware connection

System overview
Fujitsu UTY-VMSX system diagram — Modbus network topology
Electrical wiring
Fujitsu UTY-VMSX electrical wiring — RS-485 connection

The UTY-VMSX converter sits between the Modbus network (connected to TapHome) and the Fujitsu indoor unit. The Modbus cable connects to the RS-485 terminals on the converter, while the supplied 1.5 m connector cable links the converter to the indoor unit.

Technical specifications
  • Power consumption: 1.2 W (powered from indoor unit)
  • Operating temperature: 0-46 °C
  • Dimensions: 43 x 117 x 140 mm
  • Weight: 200 g
  • Protocol: Modbus RTU Slave, RS-485
  • Baud rate: 9600 bps (default) or 19200 bps
  • Parity: Even (default), Odd, or None
  • Max cable length: 1000 m
  • Max units per bus: 31 (without repeater), 247 (with repeater)
RS-485 wiring

Connect using a 3-wire RS-485 connection to the MODBUS connector (supplied accessory):

  • A+ (D+) –> A+/D+ on TapHome RS-485
  • B- (D-) –> B-/D- on TapHome RS-485
  • COM –> GND on TapHome power supply

Cable specification:

  • Type: AWG 16-26, 3-wire sheathed PVC cable
  • Use shielded cable for transmission
  • Max length: 1000 m
  • Earth (ground) the shield metal at one end of the cable
  • Tightening torque for MODBUS connector: 0.22-0.25 N*m

Important – Shielding and grounding

Use shield cable for transmission. The shield metal should be earthed (grounded) at one end. Connect the shield to the Earth (Ground) terminal on the converter. Do not connect the shield to the Common (COM) terminal.

Configuration

Enabling Modbus communication

The UTY-VMSX converter requires DIP switch configuration on the PCB before first use. Open the top cover by inserting a screwdriver into the opening hole.

Fujitsu UTY-VMSX PCB layout with DIP switches SET4-SET7 and LED indicators
PCB overview
Fujitsu UTY-VMSX PCB component location and electrical wiring diagram

Key components on the PCB:

  • SET4 / SET5 – 8-position DIP switches for Modbus slave address (1-247)
  • SET6 – Communication settings (baud rate, parity, stop bit)
  • SET7 – Terminal resistance switch (SET7-4)
  • LED5 (Green), LED6 (Orange), LED7 (Red) – Status indicators
  • Modbus Network connection port – RS-485 3-wire terminal (A+, B-, COM)

All DIP switch settings are read at power-on time. Changes made after power-on are not reflected until the next power cycle.

Slave address setting (SET4 / SET5)

The slave address is set using 8 DIP switches across SET4 (4 switches) and SET5 (4 switches). Address range: 1 to 247.

Factory default: Address 1 (SET4-1=ON, SET4-2=ON, all others OFF)

Address examples:

AddressSET5-1SET5-2SET5-3SET5-4SET4-1SET4-2SET4-3SET4-4
1OFFOFFOFFOFFOFFOFFONON
2OFFOFFOFFOFFOFFOFFOFFON
3OFFOFFOFFOFFOFFOFFONOFF
5OFFOFFOFFOFFOFFONOFFON
10OFFOFFOFFOFFONOFFONOFF

Recommended: Address 1 for the first converter (factory default).

Communication settings (SET6)
SwitchOFF (Default)ON
SET6-2 (Stop bit)1 bit2 bit (no parity)
SET6-3 (Parity)Even parityOdd parity
SET6-4 (Baud rate)9600 bps19200 bps

For TapHome: Use the default settings (9600 bps, even parity, 1 stop bit) – all SET6 switches OFF.

When the stop bit is set to 2 bit (SET6-2=ON), parity is automatically set to “None” regardless of SET6-3.

Terminal resistance (SET7-4)
SwitchSetting
SET7-4 OFF (Default)Terminal resistance disabled
SET7-4 ON120 ohm terminal resistance enabled

For TapHome: TapHome Core has a built-in 120 ohm resistor on its BUS terminals. Set SET7-4=ON only on the last UTY-VMSX converter on the bus. All other converters should have SET7-4=OFF.

Terminal resistances are needed at both ends of the Modbus communication line (total 2 resistances).

Device capabilities

Thermostat control

The Thermostat device combines room temperature monitoring and setpoint control:

  • Room temperature (I:30058) – current room temperature in °C (value / 4, resolution 0.25°C)
  • Setpoint (I:30056 read / H:40004 write) – target temperature in °C. Writing uses Fujitsu encoding with a change flag in bit 0 and temperature x 4 in bits 1-8 (resolution 0.5°C for writing)
  • Set Limits service action – writes temperature limits for Cool/Dry (H:40012-40013), Heat (H:40014-40015), and Auto (H:40016-40017) modes simultaneously
Unit power and operation mode
  • ON/OFF (I:30055 / H:40003) – starts or stops the indoor unit. Values are offset-converted: Fujitsu uses 1=Stop, 2=Operating while TapHome maps to 0=OFF, 1=ON
  • Operation Mode (I:30054 / H:40002) – selects Auto, Cool, Dry, Heat, or Fan mode
Fan speed and airflow direction
  • Fan Speed (I:30057 / H:40005) – selects from Auto, Quiet, Low, Medium, High, Medium-Low, and Medium-High
  • Vertical Airflow Direction (I:30060 / H:40006) – controls the vertical louver: Swing, Position 1-4
  • Horizontal Airflow Direction (I:30061 / H:40007) – controls the horizontal louver: Swing, Position 1-5
Energy management and protection
  • Energy Save Mode (I:30064 / H:40010) – switches between normal operation and energy save mode
  • Anti-Freeze (I:30065 / H:40011) – enables or disables anti-freeze protection to prevent pipe freezing
  • Human Detection Auto Off (I:30074 / H:40021) – enables automatic unit shutdown when no human presence is detected
Maintenance
  • Filter Sign Reset (H:40009) – push button to reset the filter maintenance indicator after cleaning or replacing the filter
Service diagnostics

The module exposes one service attribute:

  • Slave ID (I:30002) – reads the currently configured Modbus slave address from the converter
Additional capabilities

The UTY-VMSX converter also exposes registers for error monitoring (I:30059 – error flag and error code), indoor unit status (I:30069 – defrost, oil recovery, pump down), filter sign status (I:30063), temperature limits readback (I:30066-30068), external thermostat control (H:40018), remote controller lock (H:40008/I:30062), human detection auto save (H:40019-40020), auto off time (H:40022), demand status (I:30071), and converter diagnostics (I:30001, I:30003, I:30007, I:30009). These can be added in a future template update.

The error status register (I:30059) is not included in the current template. To monitor indoor unit errors, it can be added as a custom Modbus device in TapHome using input register 30059 with bit-packed error flag and error code.

LED status indicators

LEDColorFunction
LED5GreenConverter status
LED6OrangeCommunication activity
LED7RedError indicator

Normal state: LED5 green steady, LED6 off. During Modbus communication, LED6 lights orange.

Startup sequence: LED5 and LED6 flash during initialization (a few seconds after power-on). After initialization completes, LED5 lights solid green.

LED behavior patterns:

  • LED5 steady green, LED6 off – normal operation, ready
  • LED5 steady green, LED6 steady orange – Modbus sending or receiving
  • LED5 flashing (1s ON / 1s OFF) – startup sequence or address rewriting
  • LED5 flashing (x11), LED6 flashing (x1), LED7 flashing – peripheral unit main PCB error

Troubleshooting

No Modbus communication (LED6 not lighting during commands)
  1. Check RS-485 cables:
    • A+ (D+) correctly connected to A+/D+ on TapHome
    • B- (D-) correctly connected to B-/D- on TapHome
    • COM connected – most common issue
  2. Verify the Modbus slave address on DIP switches SET4/SET5
  3. Check the terminal resistance (SET7-4) – last unit on bus should have SET7-4=ON
  4. Confirm TapHome is set to: 9600 bps, even parity, 1 stop bit (matching converter defaults)
  5. Make sure the converter has been power-cycled after changing DIP switch settings
Indoor unit not responding
  1. Check the connector cable between the UTY-VMSX and the indoor unit
  2. Verify the indoor unit is powered on
  3. Restart the converter by power-cycling the indoor unit
Timing restrictions

When performing periodical settings (schedules for ON/OFF and thermostat off), allow more than 10 minutes between Start/Release and Stop/Set operations. Rapid switching may affect the outdoor unit compressor.

Available devices

Fujitsu Air Condition via UTY-VMSX Module
Service Attributes
Slave IDreads I:30002 (UInt16); Modbus slave address set on converter (1–247)
Attributemodule-level service attribute with no read formula defined in template

Fujitsu Air Condition via UTY-VMSX

Service Attributes
Slave ID
MODBUSR(A, 1,UInt16)
Atribút
Anti-Freeze Multi-value Switch

Anti-freeze protection to prevent pipe freezing during cold conditions

Register: I:30065 → H:40011 UInt16 numeric
Values / States: Bez zmeny · Uvoľnenie · Anti Freeze

Anti-Freeze

Read switch state
MODBUSR(A, 64, UInt16)
Write switch state
MODBUSW(H, 10, UInt16, Mu)
Human Detection Auto Off Multi-value Switch

Automatic unit shutdown when no human presence is detected

Register: I:30074 → H:40021 UInt16 numeric
Values / States: Bez zmeny · Detekcia vypnutá · Detekcia zapnutá

Human Detection Auto Off

Read switch state
MODBUSR(A, 73, UInt16)
Write switch state
MODBUSW(H, 20, UInt16, Mu)
Energy Save Mode Multi-value Switch

Switches between normal and energy-saving operation to reduce power consumption

Register: I:30064 → H:40010 UInt16 numeric
Values / States: Bez zmeny · Normál · Economy

Energy Save Mode

Read switch state
MODBUSR(A, 63, UInt16)
Write switch state
MODBUSW(H, 9, Int16, Mu)
Horizontal Airflow Direction Multi-value Switch
Register: I:30061 → H:40007 UInt16 numeric
Values / States: Bez zmeny · Swing · Pozícia 1 · Pozícia 2 · Pozícia 3 · Pozícia 4 · Pozícia 5

Horizontal Airflow Direction

Read switch state
MODBUSR(A, 60, UInt16)
Write switch state
MODBUSW(H, 6, UInt16, Mu)
ON/OFF Switch
Register: I:30055 → H:40003 UInt16

ON/OFF

Read switch state
MODBUSR(A, 54, Uint16) -1
Write switch state
MODBUSW(H, 2, Uint16, St +1)
Operation Mode Multi-value Switch
Register: I:30054 → H:40002 UInt16 numeric
Values / States: No change · Auto · Cool · Dry · Heat · Fan

Operation Mode

Read switch state
MODBUSR(A, 53, UInt16)
Write switch state
MODBUSW(H, 1, UInt16, Mu)
Filter Sign Reset Push Button

Push button to reset the filter maintenance indicator after cleaning or replacing the filter

Filter Sign Reset

Read button state
MODBUSR(A, 62, UInt16)
Write button state
MODBUSW(H, 8, UInt16, Bp)
Thermostat Thermostat

Room temperature monitoring and setpoint control with configurable temperature limits per mode

Register: I:30058 → H:40004 UInt16 Unit: °C numeric
Service Actions
Set limits

Thermostat

Read temperature
MODBUSR(A, 57, UInt16)/4
Read desired temperature
MODBUSR(A, 55, UInt16)/4
Write desired temperature
MODBUSW(H, 3, UInt16, ((Se*4)<<1)+1)
Service Actions
Set limits
#modbusw(H, 11, uint16, 101);
#modbusw(H, 12, uint16, 41);
#modbusw(H, 13, uint16, 121);
#modbusw(H, 14, uint16, 81);
#modbusw(H, 15, uint16, 121);
#modbusw(H, 16, uint16, 41);
modbusw(H, 11, uint16, 101, 41, 121, 81, 121, 41);
Vertical Airflow Direction Multi-value Switch
Register: I:30060 → H:40006 UInt16 numeric
Values / States: Bez zmeny · Swing · Pozícia 1 · Pozícia 2 · Pozícia 3 · Pozícia 4

Vertical Airflow Direction

Read switch state
MODBUSR(A, 59, UInt16)
Write switch state
MODBUSW(H, 5, UInt16, Mu)
Fan Speed Multi-value Switch
Register: I:30057 → H:40005 UInt16 numeric
Values / States: Bez zmeny · Auto · Tichý režim · Výkon 1 · Výkon 3 · Výkon 5 · Výkon 2 · Výkon 4

Fan Speed

Read switch state
MODBUSR(A, 56, UInt16)
Write switch state
MODBUSW(H, 4, UInt16, Mu)
Connection: Modbus RTU • 9600 baud• 8E1 • Slave ID: $[SlaveId]
Possible improvements (22)
  • I:30058 Room Temperature (standalone sensor) — Room temperature (°C × 4, resolution 0.25°C) — read by thermostat device but not exposed as standalone temperature sensor
  • I:30059 Error Status — Error flag + error code (bit0=error flag, bit8-15=error code sections). No readscript or error handling in template
  • I:30069 Indoor Unit Status — Bit-packed status: defrost, oil recovery, pump down, normal/special. Not exposed in template
  • I:30063 Filter Sign Status — 0=No sign, 1=Filter sign. Push button for reset exists but no read-back sensor for filter status
  • I:30066 Temperature Limits Cool/Dry — Upper and lower setpoint limits for Cool/Dry mode (bit-packed, °C × 4). Writable via service action but not readable as device
  • I:30067 Temperature Limits Heat — Upper and lower setpoint limits for Heat mode (bit-packed, °C × 4)
  • I:30068 Temperature Limits Auto — Upper and lower setpoint limits for Auto mode (bit-packed, °C × 4)
  • I:30070 External Thermostat Status — 1=Release, 2=Thermostat off
  • H:40008 Remote Control Lock — Bit-packed lock settings for remote controller functions (all modes, timer, temp, mode, start/stop, start, filter reset)
  • H:40018 External Thermostat Setting — 0=No change, 1=Release, 2=Thermostat off
  • H:40019 Human Detection Auto Save — 0=No change, 1=No operation, 2=Operating. Template has auto off (H:40021) but not auto save
  • H:40020 Human Detection Auto Save Time — Time in minutes with change flag (resolution 15 min)
  • H:40022 Human Detection Auto Off Time — Time in minutes with change flag (resolution 60 min). Auto off toggle exists in template but time setting is missing
  • I:30062 Remote Control Lock Status — Bit-packed read-back of remote controller lock state
  • I:30071 Demand Status — 1=No operation, 2=DRM 1, 3=DRM 2, 4=DRM 3
  • I:30072 Human Detection Auto Save Status — 0=No operation, 1=Operating
  • I:30073 Human Detection Auto Save Time Status — Time value in minutes (resolution 15 min)
  • I:30075 Human Detection Auto Off Time Status — Time value in minutes (resolution 60 min)
  • I:30009 Converter Error Monitoring — Converter-level error flag + error code (bit0=error flag, bit8-15=error code)
  • I:30001 Communication Speed Info — 0=9600 bps, 1=19200 bps
  • I:30003 Model Name — Converter model name encoded in 2 bytes
  • I:30007 Software Version — Converter software version encoded in nibbles
Download Template

Sources