STM32F103xx
Description
Clocks and startup
System clock selection is performed on startup, however the internal RC 8 MHz oscillator is
selected as default CPU clock on reset. An external 4-16 MHz clock can be selected and is
monitored for failure. During such a scenario, it is disabled and software interrupt
management follows. Similarly, full interrupt management of the PLL clock entry is available
when necessary (for example with failure of an indirectly used external oscillator).
Several prescalers allow the configuration of the AHB frequency, the High Speed APB
(APB2) and the low Speed APB (APB1) domains. The maximum frequency of the AHB and
the High Speed APB domains is 72 MHz. The maximum allowed frequency of the Low
Speed APB domain is 36 MHz.
Boot modes
At startup, boot pins are used to select one of three boot options:
●
●
●
Boot from User Flash
Boot from System Memory
Boot from SRAM
The boot loader is located in System Memory. It is used to reprogram the Flash memory by
using the USART.
Power supply schemes
●
●
●
V
DD
= 2.0 to 3.6 V: external power supply for I/Os and the internal regulator.
Provided externally through V
DD
pins.
V
SSA
, V
DDA
= 2.0 to 3.6 V: external analog power supplies for ADC, Reset blocks, RCs
and PLL. In V
DD
range (ADC is limited at 2.4 V).
V
BAT
= 1.8 to 3.6 V: power supply for RTC, external clock 32 kHz oscillator and backup
registers (through power switch) when V
DD
is not present.
Power supply supervisor
The device has an integrated Power On Reset (POR)/Power Down Reset (PDR) circuitry. It
is always active, and ensures proper operation starting from/down to 2 V. The device
remains in reset mode when V
DD
is below a specified threshold, V
POR/PDR
, without the need
for an external reset circuit.
The device features an embedded programmable voltage detector (PVD) that monitors the
V
DD
power supply and compares it to the V
PVD
threshold. An interrupt can be generated
when V
DD
drops below the V
PVD
and/or when V
DD
is higher than the V
PVD
threshold. The
interrupt service routine can then generate a warning message and/or put the MCU into a
safe state. The PVD is enabled by software.
Refer to
for the values of
V
POR/PDR
and V
PVD
.
9/67
STMICROELECTRONICS [ STMICROELECTRONICS ]
