AN4365 datasheet(25/35 Pages) STMICROELECTRONICS

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DocID025303 Rev 2

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AN4365

STM32F4 low-power application case

3.1.1

Application functional description

• Hardware description

The main STM32F4 modules used by this application are:

–

ADC peripheral: used to convert voltages coming from VBAT

–

DMA peripheral: used to transmit data from the ADC to memory, from memory to

I2C and from I2C to memory, and to reduce the CPU load

–

I2C peripheral: configured as Slave Transmitter and Master Receiver and used to

control the transmission between devices

–

RTC peripheral: used to wake-up CPU from Standby after a defined wake-up

time

–

User button: used to startup the application

Figure 12. Application modules and data flow

• Software description

This software example makes the application operate in master and slave configurations.

Two devices are connected and set up both the transmit and receive data between each

other using a common I2C bus.

The state machine in Figure 13 describes the application and the procedure of the

transmission between the two devices.

Initially, the master/slave pair remains in Standby mode.

First, the user presses the user button and the application starts. Then, the master wakes up

and wakes the slave by toggling pin PA5 (connected to slave PA0) and then enters in low-

power mode (Sleep).

Then, on the Slave side, the ADC starts conversions of VBAT voltages and the DMA stores

these converted values in memory. During this operation, the CPU stays in Sleep mode.

Once the DMA transfer is completed, the CPU wakes up just to configure the I2C slave to

start transmitting data to master and returns back to sleep mode until the slave (sensor)

finishes the transmission.

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