Hi Qiao,
take a look at this application note:
http://www.nxp.com/assets/documents/data/en/application-notes/AN5319.pdf
http://www.nxp.com/assets/documents/data/en/application-notes-software/AN5319SW.zip
It's for MPC5748G but the principle is the same also for MPC5746R.
Regards,
Lukas