ST STM32F4

Option byte programming

The STM32F4 series devices provide some option bytes which allow some "permanent" configuration as well as readout protection for the device. Unfortunately, the option bytes become effective immediately when programmed. This means when enabling the read protection of the device via option bytes, the programmer will immediately lose the access to the flash, without any possibility to verify the complete flash operation. Therefore, the option bytes cannot be programmed as part of the flash image. via J-Flash

Via J-Flash

In order to program the option bytes, some steps need to be added in J-Flash at Options -> Project settings -> CPU -> Exit Steps. These steps will be executed after Target -> Auto has completed programming the image.

The option byte values are transmitted in the step which writes the OPTCR. J-Flash comes with an example project for the STM32F405OE which demonstrates how to program the option bytes. These steps can be adapted for all STM32F2 / F4 devices since they are identical. The example can be found by selecting Create project from template, navigating to the ST folder and select STM32F405OE_OptBytes.jflash .