AT-START-F435
User Manual
2021.11.20
10
Rev
1.00
3.4
Boot mode selection
At startup, three different boot modes are available for selection through pin configuration.
Table 1. Boot mode selection jumper settings
Jumper
Pin configuration
Boot mode
BOOT1 BOOT0
JP1 to GND or be OFF
JP2 optional or be OFF
X
0
Boot from internal Flash memory (factory default setting)
JP1 to VDD
JP2 to GND
0
1
Boot from system memory
JP1 to VDD
JP2 to VDD
1
1
Boot from internal SRAM
3.5
External clock source
3.5.1
HEXT clock source
There are three methods to configure the external high-speed clock sources by hardware:
On-board crystal (Factory default setting)
On-board 8 MHz crystal is used as HSE clock source. The hardware must be configured: R1
and R3 ON, R2 and R4 OFF.
External oscillator from PH0
External oscillator is injected from the pin_23 of J2. The hardware must be configured: R2 ON,
R1 and R3 OFF. To use PH1 as GPIO, R4 ON can be connected to the pin_24 of J2.
HSE unused
PH0 and PH1 are used as GPIOs. The hardware must be configured: R14 and R16 ON, R1
and R15 OFF.
3.5.2
LEXT clock source
There are three methods to configure the external low-speed clock sources by hardware:
On-board crystal (Factory default setting)
On-board 32.768 kHz crystal is used as LEXT clock source. The hardware must be configured:
R5 and R6 ON, R7 and R8 OFF
External oscillator from PC14
External oscillator is injected from the pin_3 of J2. The hardware must be configured: R7 and
R8 ON, R5 and R6 OFF.
LEXT unused
PC14 and PC15 are used as GPIOs. The hardware must be configured: R7 and R8 ON, R5
and R6 OFF.
