Implementing and Analyzing Single Edge Nibble Transmission (SENT) Protocol for Automotive Applications

Sammanfattning: With advancement in automotive systems, it is not just the combination of mechanical devices like in old days. Almost all the systems of today's modern car are controlled electronically by a number of ECUs (Electronics Control Unit) with the combination of sensor modules. To exchange information between the ECU and sensor modules a number of communication standards are used. The most commonly used standards are CAN, LIN, and PWM etc. The data transmission between the ECU and sensor modules can be easily established with a PWM (Pulse Width Modulation) techniques in comparison with CAN or LIN. PWM provide a convenient solution in terms of cost and performance when the data-rate is up to 10-bits. While for higher resolution data rates its performance is not satisfied. Extra effort is needed to implement diagnostic information for the integrity of data. Also, the accuracy of PWM signal is dependent on the noise voltage and channel bandwidth. In 10-bit system a single bit is represented by 4mV which face serious problem in automotive system due to the noise voltage pulses which effect the resolution of the PWM. The alternative solution for safe and high data rate which is more than 10-bit resolution is to used CAN and LIN protocols. Both CAN and LIN have availability of diagnostic modes for an ensured data transmission. Also, their capabilities for interconnecting a number of nodes (sensors-modules) on the same network can significantly reduce the wiring cost. But in automotive a number of systems need to communicate through point-to-point link, and it seem to be too expensive to used CAN and LIN for point-to-point communication because of its development complexity and wiring cost for a standalone system. To overcome these issues and to provide an alternative low-cost solution the SAE (Society of Automotive Engineers) developed a 3-wire new digital point-to-point protocol called SENT. SENT (Single Edge Nibble Transmission) Protocol is now an international standard (SAE J2716). SENT is unidirectional point-to-point communication protocol, which can be used for high resolution data transmission between sensor module and ECU. The data are transmitted by sensor module in a series of pulses each pulse is 4-bit (one nibble) long and the data are measured between two falling edges by the receiving module. There are total of nine pulses which defined the SENT frame. The first pulse is called calibration pulse, it is used for compensating to recalibrate all the other pulses in case of transmitter clock deviation, this is the best feature of SENT and can be implemented in the decoder design. This thesis work focuses on the development of SENT protocol decoder and its signal robustness analysis in comparison with the conventional PWM signal. Our first goal is to developed SENT-Protocol decoder in software on the available microcontrollers is to check how much memory foot print is used and how much the processor overhead. Two platforms have been used for this purpose. First, two implementation designs prototype were made with fixed-point and floating-point development techniques on the 32-bit platform for SENT decoder. Secondly SENT-decoder were developed with 8-bit platform and compared with the two previous designs to check how much memory foot print is used and how much is the processor overhead. Finally, the signal integrity analysis has been performed for PWM and SENT signal using spice simulation. The purpose is to check the maximum data rate limit that the PWM signal support without creating any bit error in the transmitted signal. The same data rate is then used for SENT signal to be compared with PWM signal.