在做bootload时发现UBC选项字节和手册上的差别甚大，
不知道是手册错误还是设置问题
datasheet:
UBC[7:0] User boot code area
0x00: no UBC, no write-protection
0x01: Page 0 to 1 defined as UBC, memory write-protected
0x02: Page 0 to 3 defined as UBC, memory write-protected
0x03: Page 0 to 4 defined as UBC, memory write-protected
...
0x3E: Pages 0 to 63 defined as UBC, memory write-protected
Other values: Reserved
Note: Refer to the family reference manual (RM0016) section on
Flash write protection for more details.
