Doc ID 15058 Rev 3
Each channel is connected to dedicated hardware DMA requests, with support for software
trigger on each channel. Configuration is made by software and transfer sizes between
source and destination are independent.
The DMA can be used with the main peripherals: SPI, I2C, USART, general purpose timers
TIMx and ADC.
RTC (real-time clock) and backup registers
The RTC and the backup registers are supplied through a switch that takes power either on
VDD supply when present or through the VBAT pin. The backup registers are ten 16-bit
registers used to store 20 bytes of user application data when VDD power is not present.
The real-time clock provides a set of continuously running counters which can be used with
suitable software to provide a clock calendar function, and provides an alarm interrupt and a
periodic interrupt. It is clocked by a 32.768 kHz external crystal, resonator or oscillator, the
internal low power RC oscillator or the high-speed external clock divided by 128. The
internal low power RC has a typical frequency of 40 kHz. The RTC can be calibrated using
an external 512 Hz output to compensate for any natural crystal deviation. The RTC
features a 32-bit programmable counter for long term measurement using the Compare
register to generate an alarm. A 20-bit prescaler is used for the time base clock and is by
default configured to generate a time base of 1 second from a clock at 32.768 kHz.
The independent watchdog is based on a 12-bit downcounter and 8-bit prescaler. It is
clocked from an independent 40 kHz internal RC and as it operates independently from the
main clock, it can operate in Stop and Standby modes. It can be used as a watchdog to
reset the device when a problem occurs, or as a free running timer for application timeout
management. It is hardware or software configurable through the option bytes. The counter
can be frozen in debug mode.
The window watchdog is based on a 7-bit downcounter that can be set as free running. It
can be used as a watchdog to reset the device when a problem occurs. It is clocked from the
main clock. It has an early warning interrupt capability and the counter can be frozen in
This timer is dedicated for OS, but could also be used as a standard down counter. It
A 24-bit down counter
Maskable system interrupt generation when the counter reaches 0.
Programmable clock source
General-purpose timers (TIMx)
There areup to two synchronizable general-purpose timers embedded in the STM32F101xx
low-density access line devices. These timers are based on a 16-bit auto-reload up/down
counter, a 16-bit prescaler and feature 4 independent channels each for input capture,