Sleep mode is entered from the normal mode when the following conditions are met.
1.Select sleep mode. Write a 1 to can.MSR[SLEEP].
2.Wait for the CAN bus to go idle.
3.Wait for all the TXFIFO and TXHPB messages to be transmitted.
In normal mode, can.MSR[LBACK] = 0 and can.SSR[CEN] = 1. Also, can.MSR[SNOOP] = don't care.