FlexRay通信系统协议规范V2.1修订本A-第三章 编码和解码.pdf

FlexRay Protocol Specification Chapter 3: Coding and Decoding Chapter 3 Coding and Decoding This chapter defines how the node performs frame and symbol coding and decoding. 3.1 Principles This chapter describes the coding and decoding behavior of the TxD, RxD, and TxEN interface signals between the communication controller and the bus driver. A node may support up to two independent physical layer channels, identified as channel A and channel B. Refer to section 1.9.4 for additional information on the interface between the CC and the BD. Since the FlexRay protocol is independent from the underlying physical layer, the description in this chapter assumes a binary medium with two distinct levels, called HIGH and LOW.16 A bit stream generated from these two levels is called a communication element (CE). A node shall use a non-return to zero (NRZ) signaling method for coding and decoding of a CE. This means that the generated bit level is either LOW or HIGH during the entire bit time gdBit. The node processes bit streams present on the physical media, extracts frame and symbol information, and passes this information to the relevant FlexRay processes. 3.2 Description In order to support two channels each node must implement two sets of independent coding and decoding processes, one for channel A and another for channel B. The subsequent paragraphs of this chapter specify the function of the coding and decoding for channel A. It is assumed that whenever a channel-specific process is defined for channel A there is another, essentially identical, process defined for channel B, even though this process is not explicitly described in the specification. The description of the coding and decoding behavior is contained in three proce