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Full Synchronous Clock Recovery Circuit for a LIN Protocol

IP.com Disclosure Number: IPCOM000021163D
Original Publication Date: 2004-Jan-25
Included in the Prior Art Database: 2004-Jan-25

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In a LIN (local interconnect network) protocol a message frame carries synchronization and identifier information from the master task to the slaves and data information from one slave task to the other slaves. As it can be seen in Figure 1, a message frame is composed of a header which is sent by the master and a response which is sent either by the master or one of the slaves. The present text focuses on the synch_field which allows a slave to recover the clock used by the master to send the data through the frame. The recovery happens just once a frame, and if the master needs another frame, then a new clock recovery phase is required. The clock recovery phase handled by the proposed concept bases on an handshake between the master and a single slave (according to the waveforms shown in Figure 2). The core of the idea consists of forcing the relative position of the rising edges of the master clock and slave clocks. The master sends a well defined toggling bit field whose length will allow the slave to recover a more or less precise transmission clock. In many network protocols (Ethernet for instance), the master sends a "preamble" of 256 toggling bits and the slave recovers the clock through a PLL (Phase Locked Loop) based system which locks the two clocks with a defined phase relationship. By using this method it is possible to recover the transmission clock used by a master device which handles some data with one or more slaves through a LIN protocol. This kind of method and algorithm can be used for all applications where a clock recovery is required.