Electronic – Disable Read Out protection STM32

Section 2.5 of the reference manual states that the system memory (which contains the bootloader factory-loaded into the part) is activated when BOOT0 is maintained high at startup and nBOOT1 is set to 1 (BOOT1 set to 0).

Section 4.1.1 of the same manual states that the default value of nBOOT1 is indeed 1. So it seems that all you need to start the bootloader is to set the BOOT0 pin to high at startup.

Then you can execute the loaded code by setting BOOT0 to low at startup. When BOOT0 is low, the code from the embedded flash is executed irrelevant of the state of nBOOT1.

First the programming voltage, it is given in the data sheet under the operating conditions of the memory (page 63):

Vprog Programming voltage 2 - 3.6 V

So if I read your suggestion correct it might have been powered only by that coin cell during programming? This might be very very bad indeed. The controller draws a maximum current during write operation (just the flash) of 7 mA. A small coin cell really doesn't cope well with higher currents and it's voltage as well as the capacity dropped probably really fast. Given the datasheet of a CR1220, the voltage drop on a full battery would be at least 0.5 V if you draw 7 mA from it, so it starts out at about 2.35 V, not much headroom.

But I also wonder if your circuit is fine now - have you measured the current it draws and checked all the voltages and their stability if you draw current (connect a resistor decade and vary it a bit)?

Now a possibility on how you might be able to salvage the part. I guess it won't work as you have no trouble connecting to the device, but anyways:

The F103 has a built in bootloader which is accessible if you pull the BOOT pin high during power up. You will also need access to UART1 to be able to communicate with the bootloader. Have a read of section 3.4 of the reference manual. Another good resource is this document.

If you can connect to it, there is a tool (STSW-MCU005STM32 and STM8 Flash loader demonstrator (UM0462)) available from ST which allows to interface with the bootloader and erase or program the chip.