MPC5777: CANFD & CAN Bit rate calculations.

[sivakumaruppalu]

Hello ,

I'm implementing the CAN Driver for MPC5777 ,for the BIT rate calculations i assumed the SYNC value to be 1 which is standard across the Controllers.

I reviewed the application notes AN5045 which also says that SYNC value is always 1 and non programmable . But the MPC5777 reference manual specifies SYNC value as 3

[FTSEG1 + FTSEG2 + 3] & [TSEG1 + TSEG2 + 3].

When i assumed the SYNC value as 1 and calculated the BIT rate the CAN communication never worked but with SYNC value 3 it was perfect.

Can any one explain why the SYNC value is 3?

Thanks,
Siva.

[PetrS]

Hi,

The SYNC value is always 1. The AN5045 shows the bit time as SYNC_SEG+TSEG1+TSEG2.

From RM…

“The actual interpretation by the hardware of the BTP[TSEG1] and BTP[TSEG2] registers value is such that one more than the programmed value is used.”

So the AN5045’s bit time can be rewritten as SYNC_SEG + (BTP[TSEG1]+1) +( BTP[TSEG2]+1).

Finally assuming the SYNC is always 1 you get bit time as (BTP[TSEG1] +BTP[ TSEG2] + 3) if programmed values are considered.

Similarly for FD bit setting. Also note that the BRP and SJW are also programmed to be -1.

Regards,

Petr

[yalamandadosaky]

Hi Petr Stancik, I have doubt that CAN Bit time should be 8 and 25tq. But In the AN5045 document.

TSEG1 to 31 tq, TSEG2 to 8 tq plus sync_seg is 1tq.Then It is not following the ISO11898 Standard.