DocID030906 Rev 2
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UM2271
Hardware layout and configuration
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10.6.5
Program or debug when power supply not from ST-LINK/V2-1
Before connecting the USB cable from ST-LINK/V2-1 CN13 to the PC, it is mandatory to
power the board using the user USB OTG FS connector CN9 or the VIN pin of Arduino
connector CN16. Proceeding this way ensures that the enumeration succeeds thanks to the
external power source.
The following power-sequence procedure must be respected:
1.
Put a jumper in JP4 at location U5V to use power from user USB CN9 or at location
E5V to use power from VIN of Arduino connector CN16.
2. Connect the corresponding external power source.
3. Check the green LED LD8 is turned On.
4. Connect the PC to ST-LINK/V2-1 USB connector CN13.
If this order is not respected, the board may be powered by VBUS first from ST-LINK, and
the following risks may be encountered:
•
If more than 500 mA current is needed by the board, PC may be damaged or current is
limited by PC. As a consequence the board is not powered correctly.
•
500 mA is requested at the enumeration, so there is a risk that the request is rejected
and enumeration does not succeed if PC cannot provide such current.
10.7 Clock
sources
Two clock sources are used by STM32L4R9AI: one on LSE input and another on HSE input.
LSE clock source
The available clock source is
X1
, 32 kHz crystal for the STM32L4R9AI embedded RTC.
HSE clock source
The second clock source available by default is
X2
, 16 MHz crystal for the STM32L4R9AI
HSE system clock.
Note that another HSE clocking option is available on PCB: MCO output from STLINK MCU
to STM32L4R9AI HSE input. Please refer to
.
10.8 Reset
Source
The general reset of 32L4R9IDISCOVERY is active low. The reset sources are listed below:
•
Reset button B1
•
Embedded ST-LINK/V2-1, SW1 micro-switch set to On (default setting)
•
Arduino compatible connector CN16 pin 3
The general reset is connected to following peripheral reset functions:
•
STM32L4R9AI MCU reset
•
Octo-SPI Flash reset
•
MFX_V3 reset
•
Camera reset
