Dear 华 张,
I am very sorry it is not clear immediately.
The datasheet states "See the device specification if this clock output is available on this device and to which pin it might be connected."
It is a heritage that the reference manual contains "reference manual" (usually chapter one) and block guides.
The RM defines features and BG describes all possible features of the family.
I am sorry for confusing info.
Finally...the external pin for API is not implemented.