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STM32L - can't change Brownout level

Question asked by JR7777 on Jan 26, 2015
Latest reply on Feb 4, 2015 by JR7777
Hey there,

today i wanted to change the brownout level from 1 to 4, but i failed.
I'm using the STM32L151VDT6 and the following code at startup
if ((FLASH_OB_GetBOR() & 0x0F) != OB_BOR_LEVEL4){
        /* Unlocks the option bytes block access */
        /* Clears the FLASH pending flags */
        /* Select The Desired V(BOR) Level------------------------*/
        /* Launch the option byte loading and generate a System Reset */

It seems that i cannot change the BOR level this way so i tried the ST-Link Utility in which i can access the Option Bytes, too. Result: "Could not set Option bytes"
In the description of the controller i found this:
"Low power, ultrasafe BOR (brownout reset) with 5 selectable thresholds"
but in reference manual in section "Status register" i found at the end of the "User option byte" the note "These bits are read only"... so now i'am a little #confused
Is it possible to change the brownout level or not?
If possible, what am i doing wrong? #help