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Hardware layout UM1690
18/27 UM1690 Rev 3
5.12 OSC clock
By default, the STM32F072RBT6 clock source is the high-speed internal (HSI) RC
oscillator. Other clock sources are described hereunder.
5.12.1 OSC clock supply
If PF0 and PF1 are only used as GPIOs instead of clock, then SB17 and SB18 are ON and
R36 and R37 are removed (SB19 must be OFF).
•
MCO from ST-LINK (from MCO of the STM32F103). This frequency cannot be
changed, it is fixed at 8 MHz and connected to PF0-OSC_IN of the STM32F072RBT6.
The required configuration is:
–
SB19 ON and SB17 OFF
– R36 removed
• Oscillator on board (from X3 crystal, not provided). For typical frequencies and its
capacitors and resistors, refer to the STM32F072RBT6 datasheet.
The required configuration is:
–
SB17, SB18, SB19 OFF
– X3, R36, R37, C22, C23 soldered
•
Oscillator from external PF0 (from external oscillator through pin 7 of the P1
connector).
The required configuration is:
–
SB17 ON
– SB19 OFF
– R36 removed
5.12.2 OSC 32 KHz clock supply
If PC14 and PC15 are only used as GPIOs instead of clock, then SB13 and SB14 are ON,
and R34 and R35 are removed.
•
Oscillator on board (from X2 crystal, not provided).
The required configuration is:
–
SB13, SB14 OFF
– X2, C19, C20, R34, R35 soldered
•
Oscillator from external PC14 (from external oscillator trough the pin 5 of P1
connector).
The required configuration is:
–
SB14 ON
– R35 removed