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[STM32L151C6] change RDP level 1 to level 0

Question asked by chi.jumbler on Apr 28, 2015
Hi All:
 I'm a newbie for the MCU programming.
 So far, I use SWD protocol to program STM32L151C6 chip with RDP level 1.
 I want to remove RDP level 1, program, and change level 0 to level 1.
 However, I follow the unlock steps of RM0038 reference manual to unlock the flash.
 First, I unlock the PECR register and option byte block.

 then I write the '0xFF5500AA' value into the address of flash 0x1FF80000 for setting RDP level 0, and write the '0xFF870078' value into the address 0x1FF80004 for set USE default values.
 Then, I unprotect the flash by writing 0xFFFF0000 into the address of option block from 0x1FF80008 to 0x1FF8001C
 After performing above steps, I find that the flash's FLASH_OBR doesn't show the RDP level 0 bits, 0x00F000AA.
 How can I to enable the RDP level 0 immedately after changing RDP level ?

Regards ~