An overview of the ISO 15765-2 aka DoCAN Protocol
Saravana Pandian Annamalai
CEO @ Embien Technologies | Automotive | Embedded
Often referred to by various names, such as DoCAN, ISO 15765-2 protocol, and CAN-TP (CAN Transport Protocol), the Diagnostic communication over Controller Area Network is a key aspect of today's automotive diagnostics. It works to reliably and efficiently transmit diagnostic data between a diagnostic tool and the electronic control units (ECUs) of a car. This article intends to explain the ISO 15765-2/CAN-TP/DoCAN protocol by providing a full breakdown of its features, functions, and usage.
Due to the sophisticated electronic components in the modern car, it has become necessary to develop a CAN-TP or ISO 15765-2 protocol to ensure efficient diagnosis and retrieval of data for maintenance and repair. The advancement of automotive systems necessitates a standardized form of communication for diagnostics.
The ISO 15765-2 protocol, also known as CAN-TP, provides a common language for data transfer between diagnostic tools and various ECUs in a car. This standardization enables different tools and vehicles to be interoperable and makes it easier for mechanics to detect and fix vehicle issues. Additionally, given the amount of data that needs to be transferred, it is not feasible to do so via a single CAN/CAN-FD packet. This necessitates the need for a dependable transport mechanism, as outlined in the ISO 15765-2 standard.
CAN-TP Protocol in The OSI Layer Model
Gaining insight into ISO 15765-2 or CAN-TP requires comprehending its location in the OSI (Open Systems Interconnection) layer structure. The OSI model is a conceptual framework that outlines how diverse network protocols interact and exchange data with one another.
The following diagram provides a visualization of how the CAN TP Protocol aligns with the Open Systems Interconnect (OSI) Model:
The CAN-TP protocol is applicable to the transport and network layers of the OSI model, which guarantee faultless and reliable data transmission between two endpoints. By taking charge of the transport layer, the CAN-TP protocol incorporates procedures for segmentation, reassembly, and flow control of diagnostic messages, thereby allowing the transmission of packets with a maximum size of 4294967295 bytes.
Frames in CAN-TP
The ISO 15765-2 (CAN-TP) protocol has various frame kinds that help to send out diagnostic messages. These frames include the single frame, first frame, consecutive frame, and flow control frame.
A depiction of the structure of the ISO 15765-2 Protocol can be seen in the accompanying image. This frame type is used for the transmission of short diagnostic messages that can fit into one frame. It is the most basic frame type, with the complete diagnostic message included in the payload.
The ISO 15765-2 or CAN-TP protocol is used for extended diagnostic messages which cannot fit within a single frame. The first frame supplies data about the total length of the diagnostic message, while the consecutive frames convey the actual content.
For dependable transmission of multiple diagnostic messages, the CAN-TP protocol makes use of the flow control frame. This frame guarantees that the speed of transmission is regulated and the recipient side is able to manage the data being sent.
Single-Frame Communication in the DoCAN Protocol
The DoCAN protocol is an optimal choice for sending brief diagnostic messages that don't go beyond a single frame's payload capacity. This type of communication is straightforward and productive, making it suitable for real-time diagnostic situations.
The DoCAN protocol supports the transmission of information using a single frame of communication.
The payload of a single-frame message from a diagnostic tool contains all the diagnostic data, which can be extracted and processed by an ECU on the receiving end without having to use any additional frames.
A single-frame message is often utilized for diagnostic needs that necessitate a rapid answer from the engine control unit (ECU). To give an illustration, retrieving sensor measurements or asking for the state of a distinct component can be performed by employing a single-frame communication.
Multiple Frame Data Exchange in the DoCAN Protocol
When the diagnostic message is too big to fit in one frame, the DoCAN protocol allows for the transmission of larger messages by breaking them up into multiple frames. This technique of multi-frame communication enables the sending of longer diagnostic messages.
The initial step in multi-frame communication is sending a frame that holds details about the entire length of the diagnostic message. The receiver utilizes this data in order to assign enough memory for keeping the entire message.
After the initial frame, the DoCAN protocol sends a sequence of frames that each carry segments of the diagnostic message. Then, the receiver takes the frames and puts them together to form the complete diagnostic message.
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Multi-frame communication enables diagnostic tools to transmit comprehensive diagnostic data that would not fit in a single frame. This is especially advantageous when trying to acquire detailed information or conducting complicated diagnostic operations.
The FlowControl feature gives the recipient the ability to pause the sender so that reception can be delayed. Once the receiver is ready, they can then signal the sender to go on with the transmission. This mechanism serves to avoid overloading the recipient by controlling the rate of diagnostics messages that are sent. Flow control frames are transmitted from the receiving end to the transmitting end to inform it of its capacity to process incoming data.
ISO 15765-2 Protocol Network Layer Services
The ISO 15765-2 protocol is necessary for the higher-level protocols to guarantee reliable communication between diagnostic tools and ECUs. Its services enable communication between the two parties, as well as adjusting the protocol parameters. These services include:
N_USData.request : To ask for the transportation of data with segmentation if required
N_USData_FF.indication : To signal the start of a fragmented message getting to the higher layer
N_USData.indication : To give the received data to the higher layer
N_USData.confirm : To affirm to the superior layers that the requested service has been accomplished
N_ChangeParameter.request: To request the dynamic selection of specific inner parameters
N_ChangeParameter.confirm: To confirm to the higher layer that the change parameter has been accomplished.
The ability to allow upper tier services such as UDS to communicate effectively between the tester and ECU is enabled by these services.
Utilizing the CAN-TP Protocol in Unified Diagnostic Services (UDS)
The CAN-TP protocol is utilized substantially in the Unified Diagnostic Services (UDS) standard. This diagnostic communication protocol is commonly employed in the automotive industry for the purpose of diagnosing and servicing vehicles.
The CAN-TP protocol is employed by UDS to provide a secure connection between diagnostic tools and Electronic Control Units (ECUs). This system delineates a range of diagnostic services that can be accomplished on ECUs, for instance, obtaining sensor data, executing actuator tests, and collecting fault codes.
The CAN-TP protocol enables efficient execution of diagnostic services through its mechanisms for data transfer and flow control. By utilizing the advantages of both ISO 15765-2 or CAN-TP protocol and the UDS standard, technicians are able to more effectively diagnose and repair vehicles.
In Summary: The Significance Of DoCAN In Auto Diagnostics
The DoCAN protocol is one of the most important protocols in automotive diagnostics. This protocol allows for communication between the vehicle’s electronic control unit (ECU) and diagnostic tools. It is used to retrieve diagnostic data, control actuators, and reprogram control units. This protocol is the key to diagnosing and fixing problems with modern vehicles, and is necessary for ensuring safe and efficient operation.
The DoCAN protocol is essential for automotive diagnostics as it enables the connection between diagnostic tools and ECUs to be efficient and consistent. This is vital for obtaining valuable diagnostic data, which then can be used for precise fault diagnosis and effective vehicle upkeep.
Technicians can make use of the ISO 15765-2 protocol to effectively communicate with the multiple ECUs in a car, acquire necessary information, and complete diagnostic tasks. This standardized protocol allows for compatibility between diagnostic tools and vehicles, making it simpler to diagnose and mend vehicle issues.
The CAN-TP protocol is a crucial element of developing automotive systems, as it is reliable, versatile, and works with all kinds of automotive diagnostics. This makes it a must-have tool for both technicians and car manufacturers.
Embien has crafted the RAPIDSEA DoCAN stack, granting developers and OEMs the capability to speedily add the UDS stack to Linux, Android, Windows, and MCU-based bare metal systems.
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