Truma LIN Protocol (TIN)

This document describes Truma’s LIN-based protocol used for communication between Truma heating devices and control panels.

Heater Command (0x20) - Detailed heater command frame documentation
Heater Info 1 (0x21) - Temperature readings from heater
Heater Info 2 (0x22) - Power supply and boiler status
Device Discovery - Discovery and NAD assignment process
Error Handling - Error codes and status queries

Protocol Versions

Protocol	Signal IDs	Description
Legacy	0x03-0x07, 0x16	Older heaters with separate command frames
Modern (4.0)	0x17, 0x20-0x22	Modern heaters (mid-2018+) with unified command structure
Diagnostic	0x3C, 0x3D	Standard LIN diagnostic frames

Signal Frame Overview

Signal ID	PID	Direction	Protocol	Purpose
0x03	-	Master → Slave	Legacy	Air Heater Command
0x04	-	Master → Slave	Legacy	Water Heater Command
0x05	-	Master → Slave	Legacy	Fuel Command
0x06	-	Master → Slave	Legacy	Electro Command
0x07	-	Master → Slave	Legacy	Vent Command
0x16	-	Slave → Master	Legacy	Info (temperatures, status)
0x17	-	Master → Slave	Modern	Aircon Command
0x20	0x20	Master → Slave	Modern	Heater Command
0x21	0x61	Slave → Master	Modern	Heater Info 1
0x22	0xE2	Slave → Master	Modern	Heater Info 2
0x3C	0x3C	Master → Slave	Diagnostic	Master Request
0x3D	0x7D	Slave → Master	Diagnostic	Slave Response

Unknown/Unconfirmed Signals

Signal ID	Direction	Notes
0x09	Unknown	Seen in logs, purpose unknown
0x0A	Slave → Master	iNetX only, purpose unknown
0x18	Unknown	Seen payload: `FE FF FF FF FF FF FF FF`, purpose unknown
0x1F	Slave → Master	iNetX only, purpose unknown

Modern Protocol (4.0)

Used by modern Truma heating devices (mid-2018 onwards), InetX control panels, iNet X Connect remote modules, and modern Aventa air conditioning units.

Heater Command (0x20)

See heater-command for complete documentation.

Heater Info 1 (0x21)

See heater-info-1 for complete documentation.

Heater Info 2 (0x22)

See heater-info-2 for complete documentation.

Aircon Command (0x17) - Master → Slave

Controls air conditioning units on the bus (Truma Aventa and Saphir units).

Byte	Bits	Field
0-7		Unknown - AC control data

Frame structure requires further analysis.

Legacy Protocol

Used by older Truma heating devices with separate command frames for each function.

Air Heater Command (0x03) - Master → Slave

Byte	Bits	Field	Values
0	7:0	Target Temperature (low byte)	Kelvin × 10, little-endian
1	7:0	Target Temperature (high byte)
2-7		Unknown	Typically `0xFF` padding

Formula: temp_celsius = (u16_le(byte0, byte1) / 10) - 273

Special case: 0x0AAA (2730 in Kelvin × 10) = Off (0°C)

Water Heater Command (0x04) - Master → Slave

Byte	Bits	Field	Values
0	7:0	Target Temperature (low byte)	Kelvin × 10, little-endian
1	7:0	Target Temperature (high byte)
2-7		Unknown	Typically `0xFF` padding

Temp	Bytes (LE)
Off	`0xAA 0x0A`
Eco (40°C)	`0x3A 0x0C`
Hot (60°C)	`0xD0 0x0C`

Fuel Command (0x05) - Master → Slave

Byte	Bits	Field	Values
0	0	Fuel enable	0=Off, 1=On
0	1	Electro enable	0=Off, 1=On
0	2-7	Unknown
1-7		Unknown	Typically `0xFF` padding

Electro Command (0x06) - Master → Slave

Byte	Bits	Field	Values
0	7:0	Electro mode (low byte)	See table below
1	7:0	Electro mode (high byte)	See table below
2-7		Unknown	Typically `0xFF` padding

Mode	Byte 0	Byte 1
Off	`0x00`	`0x00`
900W	`0x84`	`0x03`
1800W	`0x08`	`0x07`

Vent Command (0x07) - Master → Slave

Byte	Bits	Field	Values
0	7:0	Vent mode	See table below
1	7:0	Unknown	Typically `0xFE`
2-7		Unknown	Typically `0xFF` padding

Value	Mode
`0xE0`	Off
`0xE1`	Comfort
`0xE2`	Boost
`0xF1` - `0xFA`	Level 1-10

Info Frame (0x16) - Slave → Master

Byte	Bits	Field	Values
0	7:0	Unknown	Seen: `0x00`
1	7:0	Unknown	Seen: `0x05`, `0x0F`, `0x17`
2	7:0	Room Temperature (low byte)	Kelvin × 10, little-endian
3	7:0	Room Temperature (high byte)
4	7:0	Water Temperature (low byte)	Kelvin × 10, little-endian
5	7:0	Water Temperature (high byte)
6	7:0	Unknown	Seen: `0xDB`, `0x59`, `0x77`, `0xF5`, `0xFF`
7	7:0	Unknown	Seen: `0x85`, `0x7F`

Diagnostic Frames

Standard LIN diagnostic frames using classic checksum (no PID in checksum calculation).

Master Request (0x3C)

ReadByIdentifier (SID 0xB2)

Byte	Field	Values
0	NAD	`0x01`=Single, `0x7F`=Broadcast
1	PCI	`0x06` (length)
2	SID	`0xB2` (ReadByIdentifier)
3	Identifier	See table below
4	Supplier ID (low)	`0x17` (Truma)
5	Supplier ID (high)	`0x46` (Truma)
6	Function ID (low)	Product-specific
7	Function ID (high)	Product-specific

Identifier Types

Value	Identifier
`0x00`	Product Identification
`0x01`	Serial Number
`0x20`	Firmware Version
`0x23`	Current Error (see Error Handling)

See Device Discovery for the complete discovery process.

Vendor-Specific Diagnostic (SID 0xB8) - Heating Control

Controls the overall heating active state. This frame must be sent alongside the 0x20 Heater Command frame to activate heating.

Byte	Field	Values
0	NAD	`0x01` (always single)
1	PCI	`0x06` (length)
2	SID	`0xB8`
3	Function ID (low)	`0x40` (CombiGas), `0x20` (CombiD)
4	Function ID (high)	`0x03`
5	Heating Active	`0x00`=Off, `0x01`=On
6	Unknown	Always `0x00`
7	Padding	Always `0xFF`

Heating Active Bit (Byte 5)

This bit controls whether the heater is actively heating. It must be set to 0x01 when any heating is requested (room heating, water heating, or both).

Value	Meaning
`0x00`	Heating off (idle/standby)
`0x01`	Heating active (room and/or water)

Important: The 0x20 Heater Command frame sets the target temperatures and modes, but the heater will not start until this B8 diagnostic frame is sent with byte 5 = 0x01.

Example Frames

Idle (heating off):

01 06 B8 40 03 00 00 FF

Heating active (room and/or water):

01 06 B8 40 03 01 00 FF

Function ID Variants

Bytes 3-4	Device
`40 03`	Combi Gas (Function 0x0340)
`20 03`	Combi D (Function 0x0320)
`10 03`	Combi Gas Old (Function 0x0310)
`01 03`	Combi Gas Old (Function 0x0301)

Clock Commands (Vendor-Specific)

Truma uses these vendor-specific SIDs (in the LIN reserved range 0xB8-0xFF) for clock/time synchronization with the CP Plus display.

SID	RSID	Purpose
`0xB9`	`0xF9`	Prepare Read/Write
`0xBA`	`0xFA`	Read Clock
`0xBB`	`0xFB`	Write Clock

Note: These are not standard LIN services. Per LIN 2.2A spec (Section 4.2.3.4), SIDs 0xB8-0xFF are reserved and refer to ISO 15765-3. Truma uses this range for proprietary extensions.

Frame structure and payload format are not fully documented.

Reset Command

All bytes set to 0xFF triggers error reset:

[0xFF] [0xFF] [0xFF] [0xFF] [0xFF] [0xFF] [0xFF] [0xFF]

Slave Response (0x3D)

ReadByIdentifier Response (RSID 0xF2)

Byte	Field	Values
0	NAD	Responding node
1	PCI	Length
2	RSID	`0xF2` (= SID + 0x40)
3+	Payload	Depends on identifier requested

See Device Discovery for Product Identification responses. See Error Handling for error response decoding.

Vendor-Specific Response (RSID 0xF8)

Byte	Field	Values
0	NAD	`0x7D`
1	Unknown	Seen: `0x00`, `0x01`, `0x02`
2	Unknown	Seen: `0x01`, `0x02`, `0x04`
3	Unknown	Seen: `0x00`, `0xFF`
4	Unknown	Seen: `0xFF`
5	Unknown	Seen: `0x05`

Seen response payloads:

01 02 00 FF 05
00 01 00 FF 05
01 01 FF FF FF
02 02 FF FF FF
00 04 00 FF 05

Clock Responses (Vendor-Specific)

RSID	Purpose
`0xF9`	Prepare Read/Write Response
`0xFA`	Read Clock Response
`0xFB`	Write Clock Response

See Clock Commands section above for details.

Timing

Parameter	Value
Startup break	1.3ms
Startup pause	1600ms
Between keepalive frames	60ms
Frames per keepalive block	~40
Keepalive block interval	~10s
Between control frames	40ms

Typical Control Frame Sequence

0x20 (Heater Command)
0x61 (request for 0x21) - may have no response
0xE2 (request for 0x22) - may have no response
0x3C (Diagnostic Request)
0x7D (request for 0x3D) - may have no response
Repeat…

After several cycles, responses start appearing on 0x21 and 0x22.

Checksum

Enhanced Checksum (Signal Frames 0x00-0x3B)

sum = PID + data[0] + data[1] + ... + data[7]
while (sum >> 8) sum = (sum & 0xFF) + (sum >> 8)
checksum = ~sum

Classic Checksum (Diagnostic Frames 0x3C+)

sum = data[0] + data[1] + ... + data[7]  // No PID
while (sum >> 8) sum = (sum & 0xFF) + (sum >> 8)
checksum = ~sum