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hello everyone welcome to controllers
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tech I have already covered sleep mode
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and stop mode today in this video I will
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cover the standby mode in stm32 let's
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take a look at the data sheet these are
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the common steps in other modes - other
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than these the wake up flag must be
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cleared before going to standby mode if
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the RTC is chosen then RTC wakeup flag
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we can exit the standby mode using
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wakeup pin or RTC interrupt or watchdog
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the latency of standby mode is same as
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reset when the MCU wakes up from the
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standby mode the SPF flag in the power
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control register is set we will use this
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fact to perform some operations after
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waking up from the standby let's start
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by creating a project in the cube IDE I
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am using stm32f4 for 6r II controller
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give some name to this project and click
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finish here is the cube MX first of all
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I am selecting the external crystal for
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the clock enable the UART for
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communicating with the computer pa5 is
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connected to the led enable the wake-up
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pin let's go to the clock setup I have
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eight megahertz external crystal and I
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want the system clock of 180 megahertz
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click Save to generate the project
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when the MCU wakes up all these will be
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to confirm if the system was resumed
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from standby mode we will check this SV
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flag if the flag is set means the MCU
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woke up from the standby mode
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first thing we will do is clear the flag
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next we will display this string on the
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and then toggle the LED few time with
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disable the wake-up pin wake-up pin one
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is common in all MCU wakeup pin two and
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three are supported by these
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microcontrollers only I am using wakeup
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pin one as its present in all the MCU
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and it is the pin PA zero
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now this is the procedure to enter the
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standby mode as mentioned in the
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datasheet we must clear the wake up flag
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before entering the standby
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I am going to display this string blink
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the LED for the indication this blinking
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rate is different from the initial one
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we must enable the wake-up pin before
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just to make sure now finally enter the
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include the string dot H file for string
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related operations let's build this code
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I am going to use the debugger
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as you can see when I press the reset
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the string got printed on the console
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LED blinks at 750 milliseconds delay and
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the MCU goes into the standby mode when
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the button is pressed the MCU wakes up
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and string got printed and LED blinks at
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200 milliseconds to indicate the wakeup
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same thing happens if I press the button
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we can also use the RTC to wake the
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device up I have already covered the RTC
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set up in my stop mode video in RTC wake
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up select internal wake up make sure you
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turn on the interrupts leave everything
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as it is we don't need to set the time
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this is a periodic wakeup and setting
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time doesn't affect it
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now go to the RTC initialization
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function and copy this function also
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just like we enabled the wake-up pin we
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are also going to enable the RTC wakeup
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inside the main function I have already
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explained this calculation in my sleep
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mode video you can check it out on the
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anyway this calculation is self
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explanatory I am using the periodic
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delay of 5 seconds here
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as mentioned in the datasheet if we are
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using RTC to wake the MCU up we need to
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clear the RTC wake-up flag also
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after wake up just like disabling the
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wake-up pin we must also deactivate the
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let's build this code and run it you can
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see the current consumption on the
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ammeter also right now the range is set
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at 200 milliamps when the device is
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running normally the consumption is
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around 36 milliamps but when it goes
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into the standby mode it's showing zero
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let me reduce the range to 2 milliamps
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now you won't be able to see the higher
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range but you can see the current during
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yes it's around point zero zero two
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milliamps which is 2 micro ampere this
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is extremely low consumption the MCU is
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waking up every 5 seconds because of the
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periodic wake up of RTC we can also use
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the wake-up pin to wake the controller
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you can see the SPF flag and w UF flag
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described in the datasheet now all three
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low power modes are covered in stop mode
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there is one feature called under drive
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mode it's not present in cortex m3 and
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maybe in other series also but its
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present in f4 for 6r II and I will cover
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it in few days you can use these low
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power modes according to your
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application this is it guys I hope you
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understood the video you can download
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the code from the link in the
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description have a nice day
