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#2. Setup Timer to generate Precise Delay || STM32F4 || LED Blink || NO HAL
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Sep 1, 2020
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View Video Transcript
0:10
[Music]
0:18
hello everyone
0:21
welcome to controllers tech this is the
0:24
second video in the series of
0:26
register-based programming for stm32
0:29
and today we will see how can we use
0:31
timer to generate the precise delay in
0:34
micro
0:34
and milliseconds let's start by creating
0:38
a project in kyle id
0:51
select your microcontroller here
0:57
the only files we need to add are the
0:59
cmsiscore
1:00
and the device startup files
1:06
in my previous video i covered how to
1:09
configure the clock
1:10
and today i will simply include that
1:12
header file
1:18
[Music]
1:24
we need to add the file here also
1:33
you can see the rcc config file have all
1:36
those functions
1:37
that we covered in the first video with
1:40
this setup
1:41
the system clock would be running at 180
1:44
megahertz
1:45
and this video will basically prove that
1:47
all that setup was completely fine
1:50
we will see more about this in a while
1:54
let's add the main.c file in our project
2:02
i am going to include the rcc config
2:05
file here
2:06
let's also create the main function and
2:09
a while loop inside it
2:16
now let's go to timers as i mentioned
2:20
i am going to use timer to create a
2:23
precise delay
2:25
here in the reference manual you can see
2:27
that we have advanced timers
2:29
some general purpose timers and some
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basic timers
2:33
since we only need the delay i will use
2:36
the basic
2:36
timer for this purpose i have two basic
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timers here
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timer 6 and timer 7.
2:44
i am going to use timer 6 for this
2:48
application
2:55
this is the data sheet of f446
2:58
and this is the clock diagram as you can
3:01
see here
3:02
the timer 6 is connected to a pb1 clock
3:05
whose core frequency is 45 megahertz
3:08
[Music]
3:13
now this is how my clock is configured
3:17
i have covered this in the first video
3:19
so if you don't understand
3:21
see that one first here i am using the
3:25
external 8 megahertz crystal to generate
3:27
a system clock of 180 megahertz
3:32
now if you notice here the apb1
3:35
timer clock is running at 90 megahertz
3:39
so i need to divide this 90 megahertz in
3:42
order to get the required delay
3:45
let's create a function for timer
3:46
configuration
3:49
these are the steps that we are going to
3:52
follow
3:53
first enable the timer peripheral clock
3:57
then set the prescaler and the arr
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register
4:02
and finally enable the timer
4:05
let's start with the first step in order
4:08
to enable the peripheral clocks
4:10
we need to modify the rcc registers
4:14
[Music]
4:23
rcc peripheral clock enable register
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have a bit
4:26
to control the timer 6 clock
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if you are using any other timer it
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might be present in apb2 register also
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here we need to write a one to the
4:51
fourth bit of apb1enr
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that's exactly what we are going to do
5:05
now it's time to set up the prescaler
5:08
and the ar
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if you remember the apb1 clock is at 90
5:14
megahertz
5:18
if i divided by 90 the clock will come
5:21
to 1 megahertz
5:24
a one megahertz clock means each count
5:27
by the counter will take one microsecond
5:30
and this way we can get the delay in
5:36
microsecond
5:40
to set the prescaler we will look in the
5:42
timer 6 registers
5:47
here we have the prescaler register
5:49
where we can directly input the value
5:56
this is the auto reload register which
5:58
is basically the maximum counts
6:01
the counter can have also note that
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a 1 will be added to the prescaler value
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that we will enter
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so we will subtract 1 from the actual
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value
6:17
let's enter the prescaler now i want to
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write 90 but because of that one being
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added
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i am writing 90 minus 1.
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provide the maximum a r r value
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so the counter can have a higher limit
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for the count
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now the final step is to enable the
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timer
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to do so we will look into the timer
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control register
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setting the bit zero of this register
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enables the counter
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so let's set the bit 0 of timer 6 cr1
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register
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we also need to wait for the update flag
7:17
to set
7:19
let's take a look at the timer status
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register
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here we only have one bit uif
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and this bit is set whenever the
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registers are updated
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so we will wait for this bit to set
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this completes the timer configuration
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now let's create a function to create
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microsecond delay
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here we will first set the counter to
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zero
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and then wait for the counter to reach
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the entered time
8:00
as each count by the counter takes 1
8:02
microsecond
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we will get the desired time delay
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timer 6 have a count register where the
8:09
counts are stored
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we will first set the counter to zero
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and then wait for it to reach the given
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value
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this waiting is in the blocking mode and
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hence we will get the delay
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let's write another function for the
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milliseconds
8:44
here we will just call the delay for
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1000 microseconds
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to achieve one millisecond delay time
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now let's configure the gpio clock
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i am using pin pa5 as the output for led
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here are the steps required to configure
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the gpio pin
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let's start with enabling the clock
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again we need to look into the rcc
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registers
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this time the ahb1 peripheral clock
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enable register
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here you can see the gpioa
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clock can be enabled by setting the bit
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zero of this registers
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so we will set the bit zero of the rcca
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hb1enregisters
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next we need to set the pin pa5 as
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output to do so we will take a look at
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the gpio registers
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gpio mode register is used to set the
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different functions for the pin
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here we want to set it as output
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bit 0 and 1 configures the pin 0
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bits 2 and 3 for pin 1 bits 4 and 5 for
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pin 2 and similarly
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bits 30 and 31 for pin 15.
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i want to set the pin pa 5 so i have to
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modify bits 10
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and 11.
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so basically we need to write a 0 in the
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11th position
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and a 1 in the 10th position
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i will just write a 1 in the 10th bit as
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the 11th bit is 0 by default
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next configure the output mode
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let's go back to the registers
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we have port output type register
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here we need to set what type of output
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we want
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for toggling the pin we want the
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push-pull type
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and that's why we need to write zero in
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the fifth position
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in the gpioa o type register
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write a zero in the fifth position
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next we need to select the speed of the
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pin
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we can work with even low speed here but
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i just want to explain
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how can we use higher speed for the pin
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here also two bits are configured for a
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single pin
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i want to select the fast speed so i
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need to write a 1 in the 11th position
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and a 0 in the 10th position
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so i will just write a 1 in the 11th
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position
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as the others are anyway zero
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next is the pull-up or pull-down
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selection
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we don't want any of it since we are
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going to toggle the pin
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so we need to write 0s in 10th and 11th
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positions
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i don't need to write these zeros since
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that's the reset state of the register
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but i want to show you how can we write
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zeros in more than one position
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at the same time so either you can write
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a zero in the tenth position
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and eleventh position separately
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or you can first write a one in both the
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positions
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and then negate the entire statement
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so this completes our gp io
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configuration
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now let's write the main function first
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of all
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call the system clock configuration
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then the timer configuration and gpio
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configuration
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now in the while loop first of all i
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will set the pin
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pa5
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to do so we need to look into the bsr
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register this register consists of two
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halves
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the upper bits are used to reset the pin
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and the lower bits are used
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to set the pin in order to set the fifth
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pin we need to write a one in the fifth
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position
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and in order to reset it we need to
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write a one in the 21st position
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let's set the pin pa first
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give a delay of one second
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reset the pin pa5
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i prefer using this method to reset
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instead of writing a 1
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in the 21st position
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give the delay again and that's all
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let's build the code we have no errors
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here
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before flashing it go to the options
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type in your clock frequency here
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mine is running at 180 megahertz
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go to debug select the sd link
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go to setting select connect under reset
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and select reset and run
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let's load the program into the board
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now
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as you can see here the led is blinking
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every second you can time the blinking
15:12
with the video time
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also
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[Music]
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we have a perfect one second delay
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let's change the delay time to 500
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[Music]
15:38
milliseconds
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build and flash again
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now the led is blinking every 500
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milliseconds
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let's change it to 250 milliseconds
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build and flash again
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you can see the results basically
16:26
this proves that whatever clock setup we
16:28
did in the previous video
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was correct since i programmed the timer
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based on those frequencies
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so if there was some error in the clock
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setup we wouldn't have got the exact
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delay
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like we did get this is it for this
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video
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i hope things were very clear we can use
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this delay for our upcoming tutorials
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where again i will simply include this
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file
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you can download the code from the link
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in the description
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in the next video i will cover the basic
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uart sending
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and receiving goodbye for now
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keep watching and have a nice day ahead
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