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Department of Engineering, ICT and Technologies for Energy and Transport Patent Title Limitation of bit-stuffing in a communication frame of an electronic signal. Ref. CNR 10288 Assignee(s): CNR CNR Institute: IEIIT Main Inventor: Gianluca Cena Countries: IT, EP Priority date: 17/02/2014 Abstract The bit-stuffing mechanism adopted in Controller Area Network (CAN) to encode the bit stream at the physical layer leads to an unwanted variability, or jitter, in frame transfer times, since the number of stuff bits is variable and depends on the frame content in a non-trivial way. Solutions like 8B9B and VHCC were proved to be optimal in order to prevent stuff bits in the payload of the frame. This invention makes it possible to prevent the occurrence of stuff bits in the Cyclic Redundancy Check (CRC) field as well. Doing so ensures extremely accurate and completely deterministic transfer times, regardless of the message content. This is of great importance in distributed control systems to improve their basic characteristics, such as timing accuracy and, as a consequence, quality of control. Moreover, the invention also reduces noticeably the residual error probability, hence increasing system reliability. Background CAN is used for real-time communications among devices in automotive, industrial, and embedded systems. Bit-stuffing in CAN leads to jitters in frame transfer times, which worsen the timing accuracy of distributed control applications. Several solutions to this issue were proposed in the past years, either based on statistical grounds or suitable encoders, which prevent the insertion of stuff bits by modifying the content of the data field. However, they are completely unable to cope with the CRC field. Technology By reserving 3 bits at the end of the data field (denoted as the tuning field), this invention permits steering CRC calculation to a value which does not cause the insertion of any stuff bit in the CRC field by the CAN controller. The invention aims at complementing techniques, like 8B9B, which prevent variability in stuff bits added to the other parts of the frame. Complete compatibility is ensured with legacy CAN controllers. Advantages and Applications This invention has two main advantages. Firstly, it reduces jitters, which may affect the duration of frame transmissions in CAN by up to about 20 bit times, to well below one bit time. In competing solutions, residual jitters can be as high as 4 bit times. Secondly, it reduces the residual error probability of CAN by about two orders of magnitude. It can be used in low-cost, high-precision, high-reliability real-time control systems. Development stage A highly-optimized prototype (codec), written in C for the NXP LPC2468 µC, has been implemented and tested for correctness and performance. The resulting jitter, measured at the application level, is in the order of 500ns. A testbed has been developed. 19