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You need to modify the board to enable the internal bootloader of the STM32F103.
- Start by unscrewing the front plate , and remove the board from the case.
- Remove the R28 resistor because it's disabling the bootloader standard mode and connect a 10K resistor between the boot1 pin and the ground as shown.
- Solder a wire to the Boot0 pin, and another to the VCC 3,3V pin. Connect the wires together. This can be removed after the STMDuino bootloader download
- Plug your TTL to Serial USB stick
- Plug the Miditech/Midipplus board into the USB
- Launch STM Flash loader demonstrator (if you don't have it , check the ST Micro. web site) and reset the Miditech/Midiplus board by by touching the RST tap point and the ground (for example the USB plug shield). As the chip is in bootloader mode, you will, or hear nothing...
- Connect TTL RX 1/TTL TX1 from the Miditech/Midiplus board to the TTL RX/ TTL TX of your serial USB converter. You can solder 2 wires to the pads clearly labelled on the board it self, or just hold the wires with the left hand and do the rest with the right one !
At this point, it is still time to stop. After that step, not return possible !!!!!
- Choose the serial port corresponding to your Serial to TTL interface in the list than click on "Next" in STMFlash
- You will see a red warning indicating that the firmware is protected, and going further will erase it. So, if you are really sure, click on "Remove protection". The existing Miditech/Midiplus firmware will be entirely erased.
- Click next, and choose the "midiplus4x4_boot20.bin" file (see in the root dir of the Git repository). This is the STMDUINO bootloader especially modified for the Miditech/Midiplus board to activate the USB DISC command (on PA8).
- Check "Optimize", "Global Erase", and "Verify after download", then "Next". The download will start, and if everything is ok, you will have a message confirming that the the update was done correctly.