Browse Prior Art Database

Full Synchronous Clock Recovery Circuit for a LIN Protocol

IP.com Disclosure Number: IPCOM000021163D
Published in the IP.com Journal: Volume 4 Issue 1 (2004-01-25)
Included in the Prior Art Database: 2004-Jan-25
Document File: 4 page(s) / 84K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

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.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 41% of the total text.

Page 1 of 4

S

Full Synchronous Clock Recovery Circuit for a LIN Protocol

Idea: Francesco Labate, AT-Villach

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.

The following calculations suppose that the ASIC (Application-Specific Integrated Circuit) clock frequency is equal to 1MHz, the baud rate transmission is 9600baud and with 8 bits per single data. According to the equations listed in the official documentation (LIN Specification Package - Revision 1.2), it is possible to evaluate the maximum bits length of a message frame including all the spaces between two different data fields:

        MAX THEADER T

    49413541*( _ =+=+_ =

 ) 1

.

.

HEADER

FRAME

MIN

        MAX TTFRAME N

As the field ident is 10 bits long (1 start_bit + 8 bits data + 1 stop_bit), it can be calculated how many bits (Nmax_bit) a generic LIN interface has to latch, once the recovered clock has been generated:

    17541*44*41*( _ =+=++_ =

 ) 1

 ) 1

.

.

10 (

MIN

DATA

                    ) ( _ _

      BREAK TTTTSYNC T

                       _ ++=-=-_ =

FIELD

49

39

10

SPACES

SYNC

FIELD

IDENT

MAX

MAX

HEADER

       BIT NTTTMAX T

The algorithm implemented for the clock recovery bases on time measurements between falling edges in the synch_field pattern. The calculated value must be divided by 8 and then rounded. Due to the rounding, the recovered clock waveform shifts in phase if compared to the one used by the master to send the data. The amount of this phase shift depends on the remainder of the division shown before.

Figure 2 shows a simulation with a...