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Department of Engineering, ICT and Technologies for Energy and Transport Patent Title PreveŶƟŶŐ ďŝƚ-sƚƵĸŶŐ ŝŶ the transmission of frames over commƵŶŝĐĂƟŽŶ ůŝŶes. Ref. CNR 10288 Assignee(s): CNR CNR InƐƟƚute: IEIIT Main Inventor: Gianluca Cena Countries: IT Priority date: 17/02/2014 Abstract The bit-stuĸng mechanism adopted in Controller Area Network (CAN) to encode the bit stream aƩ he physical layer leads to an unwanted variability, or jiƩer, in frame transfer Ɵmes, since the number of stuī bits is variable and depends on the frame content in a non-trivial way. SoluƟons like 8B9B and VHCC were proved to be ŽƉƟŵĂů in order to prevent stuī bits in the payload of the frame. This inveŶƟŽn makes it possible to prevent the occurrence of stuī bits in the Cyclic Redundancy Check (CRC) Įeld as well. Doing so ensures extremely accurate and completely determinisƟc transfer Ɵmes, regardless of the message content. This is of great importance in distributed control systems to improve their basic characterisƟcs, such as ƟŵŝŶŐ accuracy and, as a consequence, quality of control. Moreover, the inveŶƟŽn also reduces ŶŽƟĐĞĂbly the residual error probability, hence increasing system reliability. Background CAN is used for ƌĞĂůͲƟŵe commƵŶŝĐĂƟŽŶƐ among devices in auƚŽŵŽƟǀĞ, industrial and embedded systems. Bit-stuĸŶg in CAN leads to jiƩĞƌs in frame transfer Ɵmes, which worsen the Ɵming accuracy of distributed control applicĂƟons. Several sŽůƵƟŽŶƐ to this issue were proposed in the past years, either based on stĂƟsƟcal grounds or suitable encoders, which prevent the inseƌƟon of stuī bits by modifying the content of the data ĮĞůĚ͘ However, they are completely unable to cope with the CRC ĮĞůd. Technology By reserving 3 bits at the end of the data Įeld (denoted as the tuning Įeld), this inveŶƟŽn permits steering CRC ĐĂůĐƵůĂƟŽn to a value which does not cause the inseƌƟŽn of any stuī bit in the CRC ĮĞůĚ by the CAN controller. The inveŶƟŽn aims at complemeŶƟŶŐ techniques, like 8B9B, which prevent variability in stuī bits added to the other parts of the frame. Complete compĂƟďŝůŝty is ensured with legacy CAN controllers. Advantages and ApplicaƟons This invenƟon has two main advantages. Firstly, it reduces ũŝƩĞƌs, which may ĂīĞĐƚ the ĚƵƌĂƟŽn of frame transmissions in CAN by up to about 20 bit ƟŵĞs, to well below one bit Ɵŵe. In cŽŵƉĞƟŶg soůƵƟŽŶs, residual ũŝƩers can be as high as 4 bit Ɵŵes. 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 ƌĞĂůͲƟŵĞ control systems. Development stage A highly-opƟŵized prototype (codec), wrŝƩen in C for the NXP LPC2468 C, has been implemented and tested for correctness and performance. The resuůƟŶŐ jiƩĞƌ͕ measured at the ĂƉƉůŝĐĂƟon level, is in the order of 500 ns. A testbed has been developed and exhibited at the SPS-IPC-DRIVES Fair in Parma (May 20-22, 2014). 13