OLIMEX© 2015
STM32-P405 user's manual
CHAPTER 5 CONTROL CIRCUITY AND HARDWARE MODULES
5. Introduction to the chapter
Here you can find information about reset circuit and quartz crystals locations, the power supply circuit is
discussed.
5.1 Reset
The reset circuit is connected to pin #7 (NRST) of the STM32F405RG microcontroller. STM32-P405's
reset circuit includes R8 (10 kΩ), C28 (100nF) and a RESET button.
The RST signal can be found at an extension pin and has own row of pin holes at the prototype area –
check for the pin named “RST”.
The reset is also available at pin #15 of the JTAG connector. Furthermore, you can connect RST and
TRST of the JTAG together if you close the SMD jumper “R-T”.
The reset signal can be connected to pin #25 of the EXT1 header.
5.2 Clocks
There are two quartz crystals available on the board:
8 MHz quartz crystal Q1 is connected to pins 5 and 6 of the ARM microcontroller.
Quartz crystal Q2 is a 32768Hz RTC and it is connected to microcontroller's pins 3 and 4.
5.3 Power supply circuit
The power supply circuit of STM32-P405 allows the board to be fully powered from four locations.
1) The recommended location to power the board is the “PWR” barrel jack. You should provide
between 6V DC and 12V DC. There is a diode rectifier at this power input so you can also power
the board with 5V AC to 9V AC. The barrel jack is center positive.
2) The most used interface for powering is the USB type B connector. It works at +5V DC.
3) The board can also be powered via the on-board JTAG connector. In that case the board
re3.3V DC from the debugger tool.
4) The board can be fully powered from the extension pins (or the pin holes at the prototype area).
The best location to power the board would be the two pins at the bottom of the column of male
pins – provide b6V DC and +12V DC to the VIN pin. Double check the pin locations
before providing the power. Important: VIN signal line is connected after the diode rectifier – do
not provide negative voltage at VIN! Do not provide AC voltage to VIN!
If you want to use a back-up battery consider using the BAT_3V connector. It works with batteries
providing voltage in the (1.65 – 3.6)V range. This VBAT pin allows to power the device VBAT domain
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