6.9 Virtual COM port (VCP)
An STM32 serial interface is connected to the STLINK-V3E debug interface. The user can choose between a
USART or an LPUART interface.
The selection between USART and LPUART is performed by setting related solder bridges.
Refer to the tables below to set the USART or LPUART connection to the VCP interface
Table 10. USART1 connection
Solder bridge configuration
(1)
Feature
SB32, SB34 ON
SB24 SB26 SB31 SB33 OFF
USART1 (PA9/PA10) connected to STLINK-V3E VCP
SB31, SB33 ON
SB25 SB27 SB32 SB34 OFF
USART1 (PA9/PA10) connected to Zio, ARDUINO
®
Uno V3 D0/D1
1. The default configuration is in bold.
Table 11. LPUART1 connection
Solder bridge configuration
(1)
Feature
SB25, SB27 ON
SB24 SB26 SB31 SB33 OFF
LPUART1 (PG7/PG8) connected to Zio, ARDUINO
®
Uno V3 D0/D1
SB24, SB26 ON
SB25 SB27 SB32 SB34 OFF
LPUART1 (PG7/PG8) connected to STLINK-V3E VCP.
1. The default configuration is in bold.
By default:
• Serial communication between the target MCU and ST-LINK MCU is enabled on USART1 because this
interface supports the bootloader mode.
• Serial communication between target MCU, ARDUINO
®
Uno V3, and ST morpho connectors is enabled on
LPUART1, not to interfere with the VCP interface.
PG7 and PG8 are also connected to the ST morpho connector CN12 pins 66 (SB72) and 67 (SB73). The two
solder bridges can be removed in case of conflict between ARDUINO
®
Uno V3 and ST morpho for PG7 or PG8.
6.10
Bootloader
The bootloader is located in the system memory, programmed by ST during production. It is used to reprogram
the flash memory via USART, I
2
C, SPI, CAN FD, or USB FS in device mode through the device firmware upgrade
(DFU). The bootloader is available on all devices. Refer to the application note STM32 microcontroller system
memory boot mode (AN2606) for more details.
The Root Secure Services (RSS) are embedded in a flash area named secure information block, programmed
during ST production. For example, it enables secure firmware installation (SFI), thanks to the RSS extension
firmware (RSSe SFI). This feature allows customers to protect the confidentiality of the firmware to be provisioned
into the STM32 when production is subcontracted to an untrusted third party. The RSS is available on all devices,
after enabling the TrustZone
®
through the TZEN option bit.
The I/O PH3_BOOT0 gives external hardware access to the bootloader.
By default, this pin is set to level LOW by a pull‑down resistor, to boot on the internal flash memory. It is possible
to put this GPIO to level HIGH to boot on the system flash memory (bootloader), by connecting a 2.54‑mm pitch
jumper between the ST morpho connector (CN7) pin‑7 and VDD pin 5.
As mentioned above, USART1 on PA9/PA10 is connected by default because this interface supports the
bootloader mode.
UM2861
Virtual COM port (VCP)
UM2861 - Rev 5
page 28/49
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