Application note use case

AN4515

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DocID026482 Rev 1

2.2

STM32F411xx used peripherals

The application use case makes use of the below STM32F411xx peripherals:

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Clocks

Two clocks are used in this application:

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HSI: 16 MHz system clock source

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LSE: 32.768 kHz low-speed external crystal which drives the RTC clock

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SysTick timer

This timer is used for waiting loops or to generate timeouts (delays).

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GPIOs

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PA0: used as user pushbutton and wakeup pin from Standby mode

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PA3: set as a pin with interrupt on USART2_RX input to wakeup from Stop mode

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PA4: set as an input pin with interrupt connected to the MEMS PE4 pin (INT1) on

32F401CDISCOVERY. This pin is used to wake up the CPU from Sleep mode.

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PB8(I2C1_SCL) and PB9(I2C1_SDA) connected to MEMS PB6 and PB9

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When the microcontroller is in low-power mode, unused I/Os are placed in analog

input mode to reduce power consumption.

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DMA1

DMA1 is used to transfer data while the CPU is in Sleep mode.

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Stream0: enabled for receiving data from I2C1

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Stream6: enabled for transmitting data to USART2

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Unused streams are disabled

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RTC

The RTC is an independent timer/counter that provides a calendar with subseconds,

seconds and minutes to generate timestamp events.It uses the LSE clock.

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I2C1

The I2C1 interface receives data (11 samples) from the sensor at a speed up to

400 KHz.

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USART2

The USART2 is used to transfer messages to USB virtual comport through the DMA.

The USART2 is configured as follow:

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Word Length = 8 bits

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Stop Bit = one Stop bit

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Parity = without parity

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Baud rate = 9600 bauds

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Hardware flow control disabled (RTS and CTS signals)

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RAM

A specific routine is executed from RAM when the Flash memory is switched off.