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OLIMEX© 2016
STM32-H405 user's manual
Refer to the "STM32 microcontroller system memory boot mode" document ("AN2606") for more
information about the bootloader available on STM32F4xx microcontrollers.
6.4.2 R-T jumper
If you close this jumper RST and TRST at the JTAG will be connected.
The default R-T position is open.
6.4.3 VBAT signal and jumper
The VBAT pin supplies the RTC, the backup registers and the backup SRAM. This VBAT pin
allows to power the device VBAT domain from an external battery, an external supercapacitor, or
from VDD when no external battery and no external supercapacitor are present. VBAT operation is
activated when VDD is not present. The VBAT pin supplies the RTC, the backup registers and the
backup SRAM. By default VBAT jumper is closed which connects the VBAT microcontroller pin to
the 3.3V line of the board.
VBAT signal is available at pin #23 of EXT1 header – this is a good place to connect a back-up
battery that provides voltage in the (2.0-3.3)V range but you would need to open VBAT jumper!
Important! Be careful when you have battery for VBAT and another source of power applied to the
board simultaneously. If you connect additional battery to the VBAT line on the EXT1 header
without opening the VBAT jumper you would damage the board – the battery voltage would meet
the 3.3V line! You can disconnect the jumper and place two opposing Schottky diodes – one on the
pads of the jumper and the other between the battery and the EXT pins. This would allow you to use
simultaneously external power supply and back-up battery. The diodes should be something like
1N5817, 1N5818, 1N5819.
Please find more information about VBAT in the user's manual of STM32F405RG.
The default VBAT position is closed.
6.4.4 LED_E
Opening this jumper will disable the user LED.
The default position is closed.
6.4.5 USBP_E
Opening this jumper would disable the option to power the board from the USB connector.
The default position is closed.
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