Event triggering and periodic transmission are applicable only in UDS. Error memory management. In contrast, UDS provides event-driven and periodic services, for which the number of requests and responses can differ greatly. Transfer of measurement values For the transfer of measurement values, only the two-byte dataIdentifiers are available with UDS.
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The demand for a more accurate, standard and efficient fault detection in vehicle diagnostics, has led to breakthrough innovations and developments. Evolution of Vehicle Diagnostics: Earlier, there were flash codes wherein technicians had to look for flashes and convert them to codes or sometimes the technician had to physically remove vehicle components, disconnect wires for fault detection.
The increasing complexity of vehicle systems over the time mandated the need for diagnostics standards to efficiently track their scope and relevance. To cater to this need of the hour, various vehicle diagnostic protocols were conceptualized and developed. ISO and SAE Society of Automotive Engineers introduced various diagnostic protocols and standards, designed to cater to the different types of automotive ECU systems and diagnostics specifications from the vehicle manufacturers.
Image credit: nextews. The KWP protocol uses a physical layer, identical to ISO , for bidirectional serial communication over K-line with the controller. The average data rate of KWP is between 1. The maximum size of message supported within UDS is up to 8 bytes. UDS as a diagnostic protocol was developed to unify all the diagnostics standards that existed previously and to come up with a single valid set of diagnostic services for the automotive ECUs. This has ensured that integration of the UDS protocol stack reduces the additional costs for the development of diagnostic communication applications.
KWP is highly preferred where the vehicles are based on legacy systems such as K-line. Otherwise, these days UDS protocol is the go to standard for vehicle diagnostics. Transfer of Key Measurement Values: Both the diagnostic protocol facilitate exchange of request and command messages from the test equipment to the automotive ECU; and key measurement values data in response from the vehicle ECU. This means increased efficiency of data exchange.
Diagnostic Communication between Test equipment and vehicle ECU: The exchange of messages between testing device and the vehicle ECU forms the basis of the diagnostic system. The natures of request and response messages and data transfer interval between them form an important factor in vehicle diagnostics. KWP favors symmetrical communication sequence where the number of request and response messages between the testing device and server are symmetrical.
On the other hand, UDS is based on an event driven and periodic communication sequence. This means, the number of request and response messages can be different. Moreover, in a periodic communication sequence based on UDS standard, the test equipment sends periodic requests for updated information from automotive ECUs.
This helps in closely monitoring vehicle condition in regular intervals. The vehicle ECU may respond to the periodic request with one or several data record values. Thus UDS offers more detailed information related to the fault through periodic update.
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