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Boot problem STM32F042

Question asked by schnider.simon on Sep 5, 2015
Latest reply on Sep 5, 2015 by Clive One
Dear all

I have a boot problem with the STM32F042G4U6 (uVision V5.14.0.0.). I designed a custom board and sadly forgot to connect the Boot0 (floating) to GND. Because of that, I can program the MCU, but the controller don’t starts my program...

In the Reference manual (RM0091), Page 52 I found some information about booting options. The table 3 shows me, that I can set the boot option also by BOOT_SEL and nBOOT0, independent of the Boot0 Pin level. Further, I found the corresponding Bits in the Flash Option byte register (FLASH_OBR). BOOT_SEL -> Bit 15 of FLASH_OBR, nBOOT0 -> Bit 11 of FLASH_OBR.

Now my big question: Where and how can I change this two Bits, before start up? Has anybody an idea or did this before? For me it’s really important to solve this problem!

My guess is, that I have to change something in the startup file (startup_stm32f042.s). But I don’t have the view about this file… I already activated the Configuration Wizard in the startup File, but there are no information about startup.

Thanks for your help,