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VW Transport Protocol 2.0 (TP 2.0) for CAN bus

CAN allows for data packets with a payload of up to 8 bytes, to send messages longer than 8 bytes it is necessary to use a transport protocol. The OBD-II specification for example makes use of ISO-TP (ISO 15765-2). Volkswagen however uses it's own transport protocol in its vehicles, known as VW TP 2.0.

This page gives a run down on how TP 2.0 works. Please note that there is an older VW TP 1.6 which was used in some vehicles. TP 1.6 is fairly similar but some of the parameters are fixed. Its also worth noting that I have worked all of this out from various presentations and documents that I have found on the net and from logging data. I have not had any access to the official documentation from VW so take any information with a grain of salt.

Typically the payload of TP 2.0 will be ISO 14230-3, Keyword Protocol 2000 (KWP2000) application layer messages.

The four message types
TP 2.0 works by opening data "channels" between two communicating devices. Once a channel is opened data packets can be exchanged by the two devices. To do this TP 2.0 uses four message types - broadcast, channel setup, channel parameters and data transmission.

Broadcast
The broadcast type has a fixed length of 7 bytes. It is sent 5 times in case of packet loss. Not sure what it is actually used for yet.

Byte 0 1 2 3 4 5 6
Description Dest Opcode KWP Data Resp Req Resp Req
Field description

Field Description
Dest Logical address of destination module, e.g. 0x01 for the engine control unit
Opcode 0x23 Broadcast request
0x24 Broadcast response
KWP Data KWP2000 SID and parameters
Resp Req 0x00 Response expected
0x55 or 0xAA No response expected
Channel setup
The channel setup type has a fixed length of 7 bytes. It is used to establish a data channel between two modules.

The channel setup request message should be sent from CAN ID 0x200 and the response will sent with CAN ID 0x200 + the destination modules logical address e.g. for the engine control unit (0x01) the response would be 0x201.

The communication then switches to using the CAN IDs which were negotiated during channel setup.

You should request the destination module to transmit using CAN ID 0x300 to 0x310 and set the validity nibble for RX ID to invalid. The VW modules seem to respond that you should transmit using CAN ID 0x740.

Byte 0 1 2 3 4 5 6
Description Dest Opcode RX ID V RX Pref TX ID V TX Pref App
Field description

Field Description
Dest Logical address of destination module, e.g. 0x01 for the engine control unit
Opcode 0xC0 Setup request
0xD0 Positive response
0xD6..0xD8 Negative response
RX ID Tells destination module which CAN ID to listen to
RX Pref RX ID Prefix
TX ID Tells destination module which CAN ID to transmit from
TX Pref TX ID Prefix
V 0x0 CAN ID is valid
0x1 CAN ID is invalid
App Application type, seems to always be 0x01 (maybe only for KWP)
Channel parameters
The channel parameters type has a length of 1 or 6 bytes. It is used to setup parameters for an open channel and to send test, break and disconnect signals

You should send a parameters request straight after channel setup using the CAN IDs negotiated.

Byte 0
Description Opcode
OR

Byte 0 1 2 3 4 5
Description Opcode BS T1 T2 T3 T4
Field description

Field Description
Opcode 0xA0 Parameters request, used for destination module to initiator (6 byte)
0xA1 Parameters respsonse, used for initiator to destination module (6 byte)
0xA3 Channel test, response is same as parameters response. Used to keep channel alive. (1 byte)
0xA4 Break, receiver discards all data since last ACK (1 byte)
0xA8 Disconnect, channel is no longer open. Receiver should reply with a disconnect (1 byte)
BS Block size, number of packets to send before expecting a ACK response
T1 Timing parameter 1, time to wait for ACK. T1 should be greater than 4*T3
T2 Timing parameter 2, always 0xFF
T3 Timing parameter 3, interval between two packets
T4 Timing parameter 4, always 0xFF
Timing parameters

Bits 7 6 5 4 3 2 1 0
Description Units Scale
Field description

Field Description
Units 0x0 0.1ms
0x1 1ms
0x2 10ms
0x3 100ms
Scale Number to scale the units by
Data transmission
The data transmission type has a length of 2 to 8 bytes. It is used for the transmission of actual data/payload bytes.

Data transmission should only occur after channel setup and parameter negotiation.

Byte 0 1 2 3 4 5 6 7
Description Op Seq Payload
Field description

Field Description
Op 0x0 Waiting for ACK, more packets to follow (i.e. reached max block size value as specified above)
0x1 Waiting for ACK, this is last packet
0x2 Not waiting for ACK, more packets to follow
0x3 Not waiting for ACK, this is last packet
0xB ACK, ready for next packet
0x9 ACK, not ready for next packet
Seq Sequence number, increments up to 0xF then back to 0x0
Payload KWP2000 payload. The first 2 bytes of the first packet sent contain the length of the message.
Example
This example shows how to open a channel to and read measuring block 1 from the engine control unit. Data values and the CAN IDs are in hex.

CAN ID Data Format Description
200 01 C0 00 10 00 03 01 Chan setup Initiate channel setup with ECU module, request it use CAN ID 0x300
201 00 D0 00 03 40 07 01 Chan setup ECU module replies, says to use CAN ID 0x740
740 A0 0F 8A FF 32 FF Chan param Tell ECU module to send 16 packets at a time, and set timing parameters
300 A1 0F 8A FF 4A FF Chan param ECU module responds with its parameters
740 10 00 02 10 89 Data Last packet, expecting ACK. Length is 2 bytes. Send KWP2000 startDiagnosticSession request 0x10 with 0x89 as a parameter
300 B1 Data ECU sends ACK response.
300 10 00 02 50 89 Data Last packet, expecting ACK. Length is 2 bytes. ECU sends KWP2000 positive response to startDiagnosticSession
740 B1 Data We send ACK response.
740 11 00 02 21 01 Data Last packet, expecting ACK. Length is 2 bytes. Send KWP2000 readDataByLocalIdentifier request 0x21 with 0x01 as a parameter
300 B2 Data ECU sends ACK response.
300 21 00 1A 61 01 01 00 00 Data Packet to follow, not expecting ACK. Length is 26 bytes. ECU sends KWP2000 positive response to readDataByLocalIdentifier followed by the requested data
300 22 27 00 00 22 00 80 1A Data Packet to follow, not expecting ACK. KWP2000 data continued.
300 23 32 4B 25 02 7A 25 00 Data Packet to follow, not expecting ACK. KWP2000 data continued.
300 14 00 25 00 00 25 00 00 Data Last packet, expecting ACK. KWP2000 data continued.
740 B5 Data We send ACK response.
740 A8 Chan param We send disconnect.
References
Vehicular Networks - Protocols Part 1
CAN-based Higher Layer Protocols
Programming interfaces for embedded networks .. using the example of CAN (German)
Diagnostics of electronic control units (Czech)