---
title: MHI_XY_ATA_MODBUS – Modbus description
description: "### Introduction The ClimateControl for Mitsubishi Heavy Industries is suitable to interface between PAC and RAC with a XY-bus and wired EIA-485/MODBUS RTU. Each indoor unit needs one interfaces. A maximum of 63 interfaces can be connected on the same…"
url: "https://protoart.net/knowledgebase/mhi_xy_ata_modbus_description/"
updated: "2026-09-28"
category: Mitsubishi Heavy Industries
---

# MHI_XY_ATA_MODBUS – Modbus description

### Introduction

The ClimateControl for Mitsubishi Heavy Industries is suitable to interface between PAC and RAC with a XY-bus and wired EIA-485/MODBUS RTU.

Each indoor unit needs one interfaces. A maximum of 63 interfaces can be connected on the same modbus network.

ClimateControl can act as both XY-master(no wired remote connected) as XY-slave(with wired remote connected).

### **Baudrate selection**

The ClimateControl uses an auto-baud algoritm and does not require the user to set the baud rate. As the ClimateControl needs to sense the baud rate after boot, the master must send several data requests to the ClimateControl.

Supported baud rates are: 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200.
By default 8N2(8 databits, no parity and 2 stopbits). The interface can also automatically detect 8N1.

### Dip switches

There is one row of dip switches at the front of the device to hard code certain settings.

| switch | Description |
| --- | --- |
| 7 | Reserved |
| 8 | Reserved |

### **Modbus Slave Address**

The modbus address can be set between 1 and 63. Address 0 is reserved as modbus broadcast address.

| Addr | SW 1→6 | Addr | SW 1→6 | Addr | SW 1→6 | Addr | SW 1→6 |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 0 | -- | 16 | 000010 | 32 | 000001 | 48 | 000011 |
| 1 | 100000 | 17 | 100010 | 33 | 100001 | 49 | 100011 |
| 2 | 010000 | 18 | 010010 | 34 | 010001 | 50 | 010011 |
| 3 | 110000 | 19 | 110010 | 35 | 110001 | 51 | 110011 |
| 4 | 001000 | 20 | 001010 | 36 | 001001 | 52 | 001011 |
| 5 | 101000 | 21 | 101010 | 37 | 101001 | 53 | 101011 |
| 6 | 011000 | 22 | 011010 | 38 | 011001 | 54 | 011011 |
| 7 | 111000 | 23 | 111010 | 39 | 111001 | 55 | 111011 |
| 8 | 000100 | 24 | 000110 | 40 | 000101 | 56 | 000111 |
| 9 | 100100 | 25 | 100110 | 41 | 100101 | 57 | 100111 |
| 10 | 010100 | 26 | 010110 | 42 | 010101 | 58 | 010111 |
| 11 | 110100 | 27 | 110110 | 43 | 110101 | 59 | 110111 |
| 12 | 001100 | 28 | 001110 | 44 | 001101 | 60 | 001111 |
| 13 | 101100 | 29 | 101110 | 45 | 101101 | 61 | 101111 |
| 14 | 011100 | 30 | 011110 | 46 | 011101 | 62 | 011111 |
| 15 | 111100 | 31 | 111110 | 47 | 111101 | 63 | 111111 |

### Line Termination

When line termination is required, a 120 Ohm termination can be enabled with the dip switch next to the 2-pin connector. The line temination is off by default.

### Modbus Registers

The ClimateControl supports below modbus holding registers for controlling the airconditioner.

| Re**gister Address** | read / write | description |
| --- | --- | --- |
| 0 | R/W | Power On/Off 0: off 1: on |
| 1 | R/W | Mode 0: Auto 1: Heat 2: Dry 3: Fan 4: Cool |
| 2 | R/W | Fan speed 0: Auto 1: Low 2: Mid 3: High 4: Powerful |
| 3 | R/W | Vane Position 1: Position 1 2: Position 2 3: Position 3 4: Position 4 10: Swing |
| 4 | R/W | Temperature Setpoint ºC /x10ºC |
| 5 | R | Return air temperature ºC /x10ºC |

### Operational parameters and information

| **REGISTER ADDRESS** | **READ / WRITE** | **DESCRIPTION** |
| --- | --- | --- |
| 22 | R/W | External Temperature sensor (modbus) ºC /x10ºC |
| 23 | R | Temperature input 0: Internal 1: Wireless sensor 2: External source |
| 24-25 | R | Manufacturing date |
| 26 | R | Bootloader version (/10) |
| 27-34 | R | Device Serial ID (in ascii) |
| 35-41 | R | Hardware Version |
| 42 | R | Modbus Slave address |
| 43 | R | Modbus Baud rate 0 = 2400 1 = 4800 2 = 9600 (default) 3 = 19200 4 = 38400 5 = 57600 6 = 76800 7 = 115200 |
| 44 | R | Firmware version 30427 = 3.4.27 |
| 45 | R | System Status |
| 46-47 | R | Uptime In seconds |
| 48 | R | ClimateControl system status |
| 49 | R | External Thermometer - Temperature ºC /x10ºC |
| 50-55 | R | External Thermometer - Name |
| 56 | R | External Thermometer - Humidity % rh |
| 57 | R | External Thermometer - Signal Strength |
| 58 | R | External Thermometer - Last Message |

### Configuration registers

Settings and behaviour of the ClimateControl can be set by writing to the corresponding MODBUS register

| **REGISTER ADDRESS** | **READ / WRITE** | **DESCRIPTION** |
| --- | --- | --- |
| 100 | R/W | Temperature representation ¹ 0 = ºC x10 (default) 1 = ºC |
| 101 | R/W | Temperature scale ¹ 0 = Celsius (default) 1 = Fahrenheit |
| 102 | R/W | Cooling Min setpoint ¹ ºC /x10ºC |
| 103 | R/W | Cooling Max setpoint ¹ ºC /x10ºC |
| 104 | R/W | Heating Min setpoint ¹ ºC /x10ºC |
| 105 | R/W | Heating Max setpoint ¹ ºC /x10ºC |
| 106 | W | Firmware Update 1: Reboot to bootloader to check for firmware update (wifi setup required) |
| 107 | W | Reboot 1: Normal Reboot |
| 108 | W | External sensor pairing 1: Start pairing |
| 109 | R/W | XY Main / Sub ¹ 0: Interface is Sub (default) 1: Interface is Main |

¹ Value is stored in non-volatile memory

 

 

### Register explanation

**Register 5 - Return air temperature**

This register shows the return air temperature as reported by the indoor unit

**Register 22 - External Temperature Sensor**

The user can send the actual room temperature over modbus to the indoor unit. This will then be used as the temperature reference.

**Register 100 - Temperature representation**

The default setting is x10ºC. This means that the value from the register should be divided by 10. For example, 245 means 24.5ºC. This can be adjusted to round to whole numbers. 24.5ºC will then be rounded to 25ºC.

**Register 102**, **103, 104, 105 - Temperature setpoint limits**

The temperature setpoint can be limited by the system. When a user changes the setpoint using a remote or with a wall thermostat, the ClimateControl will adjust the setpoint based on this limit.

**Register 106 - Firmware Update**

When this register is set to 1, the ClimateControl will restart to it's factory bootloader to check and update new firmware. If no firmware is available, it will automatically return to normal operation. When no wifi credentials have been setup or the module is not able to connect to a wifi accesspoint, it will create it's own accesspoint as "Factory - XXXXXX" A user can connect to it and browse to http://10.0.0.1/ to setup wifi credentials.

During normal operation, wifi is turned off.

**Register 108 - External sensor pairing**

When this register is set to 1, the ClimateControl will start scanning for new sensors. The scan takes about 30 seconds. After this time it will use the sensor with the strongest signal as new sensor and store this into non-volatile memory.

**Register 109 - XY Main / Sub**

The ClimateControl can function both as Main and as Sub. If there is already a wall thermostat on the XY-bus but, then ClimateControl is usually set as sub(default). If there is no other device connected to the XY-bus, set ClimateControl as main.