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[Flexray]_Regarding 40 MHz cyrstal frequency

Question asked by yadunandan kasu on Apr 16, 2010
Latest reply on Apr 22, 2010 by yadunandan kasu

Dear everyone,

 

I have a doubt in flexray. I have a board with MPC5517G including the Flexray transceivers and with 40MHz crystal.

And my flexray node's baudrate is 10MBPS. 

So, according to the standard equation ..the time to transmit a single bit to the network can be calculated as below

1bittime = (n)*(sample clock period)  ---- EQ1

where

'1bittime':  in my case is 1/10MBPS = 0.1us

'n' is nothing but the 'cSamplesPerBit' which is flexray protocol constant value of '8'.


so, if I replace the above two values in EQ1, I get the 'sample clock period' of

 sample clock period   = (0.1us)/8

 = 0.0125us

 

But my crystal clock is only 40MHz, from which I can get only 0.025us as sample clock period... 

 

So, my doubt is, according to the standard calculation , the 'sample clock period' must be 0.0125us in this case. But my crystal clock supports only 0.025us.. but still my flexray communication is working very fine.. I mean, both Tx and Rx are going very fine. So, I'm wondered how this is occurring.

 

So, can somebody please suggest me the answer~~


thank you~

nandu

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