CAN Bit time in MPC5777M

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CAN Bit time in MPC5777M

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yalamandadosaky
Contributor V

Hi I am working with MPC5777M EVB and developing CAN Driver for it. I have doubt in CAN Bit time.As per AN5045 Document TSEG1 = 31tq, and TSEG2 = 8tq. and total time quanta per bit is 40tq.

But this is not satisfies ISO11898 standard (CAN Bit time quanta should be between 8 and 25 tq).

Can any one answer why it is like this. If i am wrong please correct it .PetrSmartinkovar

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PetrS
NXP TechSupport
NXP TechSupport

Hi,

When the bit rate switching is enabled it is recommended to use the same time quantum for both the nominal (arbitration) and data phase. Since short data time quanta are needed to enable a short data bit time, and the same time quantum should be used in the nominal bit time, the number of time quanta in a nominal bit time needs to be increased in a CAN FD network compared to a classical CAN network.

Thus ISO 11898-1 now allows more than 8 tq for each of the bit time segments Prop_Seg, Phase_Seg1 and Phase_Seg2.

The maximum can vary depending on vendors implementation.

The MPC5777M’s MCAN increases the configuration range to 16 tq for Phase_Seg2 and to 64 tq for the sum of Prop_Seg and Phase_Seg1. So the nominal bit time can be programmed in the range of [4....81] time quanta.

BR, Petr

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yalamandadosaky
Contributor V

Hi PetrS, Thanks for your reply, I am going to use CAN mode only not CAN FD mode. As per AN5045 for CAN FD the TSEG1 and TSEG2 are set to 31 and 8 respectively . So which values I can configure in CAN mode (No FD).

So can you please help me how to configure ?

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yalamandadosaky
Contributor V

Hi  PetrS, Can I use same values(TSEG1 =31 and TSEG2 =8) for the CAN mode also ?

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