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CAN problems STM32F427IIT6

Question asked by van_kuilenburg.jan on Oct 20, 2014
Latest reply on Oct 21, 2014 by Clive One


We have a new pcb with a STM32F427IIT6 processor

I have 2 strange problems with the CANbus:

A: CAN2 is not working correctly. I initialize only the CAN2, not CAN1. When I send a message, the CAN2 put a undefined message on the bus. The bittiming is okay. But the data is undefined. The problem is that the sTxMailBox is not updated to the value that is written into the registers. The  sTxMailBox is not pending, all the TMEx bits are high. The other status bits are okay and changes correctly when I send a message. The problem is solved when I activate the clock of CAN1, only the clock, not the init of CAN1. Whats the relation between the CAN1 clock and the CAN2?

B: Both CANs give sometimes a form-error on the bus. The send messages are put on the bus, but the bus is instable. It gives a lot of form-errors. The bittiming is okay, I measured with the scope. The system clock runs with 180Mhz and the APB1 with 45 Mhz. When I reduce the system clock to 168 Mhz and the APB1 to 42 Mhz (and the can-bittiming reg.), the bus is okay. There are no form-errors. Its look like that the CANblock can not runs with 45Mhz. Why not?