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STM32 TIMERS #5. Master Slave Synchronization using the TRIGGER MODE
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Dec 24, 2022
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View Video Transcript
0:01
[Music]
0:09
hello and welcome to controllers Tech I
0:13
have decided to continue the SDM 32
0:16
timer series and I will try to cover as
0:18
many timer functions as possible I have
0:21
already made a few videos in the past
0:24
which are available in the SDM 32 timer
0:26
playlist and this video will continue
0:29
that series with few more coming in the
0:31
upcoming
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weeks so far we have seen how to use pwm
0:36
input capture and encoder mode in the
0:40
timers this video will cover how to
0:42
synchronize the
0:44
timers there will be more videos coming
0:46
under the topic timer synchronization
0:49
and each of them will focus on only one
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specific
0:52
operation so today's video will cover
0:55
how to use the master timer to start the
0:57
slave timer this can help you to avoid
1:00
delay between the timer
1:03
outputs for example if you want to send
1:06
the different pwm signals to different
1:09
inputs of a device but they must all
1:11
start at the same time using the
1:14
traditional method will have some delay
1:16
between these signals as each statement
1:19
takes some time to
1:21
execute today's video will cover this
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issue and how we can use the timer
1:26
feature to avoid this delay all right
1:29
right let's start the cube idid and
1:32
create a new
1:34
project I will explain the requirements
1:36
as we go along with the
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video I am using the SDM 32f 446 re
1:44
controller give some name to the project
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and click
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finish I am enabling the external
1:51
Crystal to provide the clock to the SDM
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32 board the board has 8 MHz Crystal on
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it and lets run the system at a Max
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maximum 180 MHz
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frequency now before we proceed further
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let me show you how we can achieve this
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here you can see a diagram for
2:11
triggering the timer 2 with the update
2:13
of the timer
2:15
one basically when the counter of the
2:17
master timer that is timer one overflows
2:21
an update event will be
2:23
generated with this update event the
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slave timer that is timer 2 counter will
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start
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counting remember that the slave counter
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does not reset to zero before counting
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starts it will just resume the counter
2:37
from wherever it was
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paused this is called the trigger mode
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when the timer is used as a slave timer
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now the question is which timer will
2:48
exactly start
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counting to understand this you need to
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open the reference Manual of your
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controller and search for the internal
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trigger connection
3:04
here is one connection table but this is
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not what I am looking for this is the
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one I need as it has the timers I am
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going to work with the First Column is
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the slave timer and the rest of the
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columns represent the signal sent by the
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corresponding Master timer for example
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if timer 2 is used as the slave then
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timer 1 can be used as the master and
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the signal sent by the timer 1 will be
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it0 similarly timer 3 can also be
3:35
controlled by the timer one using the
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it0 but if you want to control the timer
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3 with timer 2 then you need to use the
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itr1 signal also I am going to use the
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pwm output to monitor the timers working
3:51
so we need to also see the clocks the
3:53
timers are running at here in the clock
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diagram you can see the apb2 timer clock
3:59
is running at 180 MHz whereas the apd1
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timer clock is at 90
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MHz this is the picture from the F 446
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re data sheet and here it is mentioned
4:12
that the timer 2 is connected to apb1
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bus whereas the timer 1 connected to the
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apb2
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bus this means the timer 2 will by
4:22
default run at 180 MHz and timer 1 will
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run at 90
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MHz we will further divide these clocks
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to reduce them all right let's set up
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the timers now timer one is the master
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timer so I am only enabling the pwm
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output on channel one the clock is at
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180 MHz so we will bring it down to 100
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HZ using the prescaler and auto reload
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value as shown in the
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formula there is no particular
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requirement for the frequency just set
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it to what you want
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next in the trigger event selection
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choose the update
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event this will generate the update
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event flag whenever the counter
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overflows in the pwm section set the
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duty cycle so that we can see the output
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in the
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oscilloscope I am setting it to 300 with
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ARA being thousand the duty will be
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30% here I am choosing the channel
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polarity to be low so the output will be
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inverted I am doing this so that we can
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see details more clearly on the
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scope this is it for the master setup
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let's set the slave timer now here in
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the slave mode select the trigger mode
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and the trigger sour is it
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r0 as I have already explained the
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trigger mode allows the master timer to
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control the start of the slave timer it0
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is the trigger signal used by the timer
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one to control roll the timer to to see
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how the slave timer behaves we will also
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enable the pwm output for the timer
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2 here we have the pin pa0 as the timer
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2 pwm pin and pa8 as the timer 1 pwm
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pin I am entering a random value here as
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the pwm is not the priority for us here
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you can see the trigger mode is selected
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as the slave controller
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just give some random value to the pulse
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also at last I am keeping the channel
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polarity low so this is it for the cube
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MX setup click save to generate the
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project in the main function we will
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just enable the pwm for both the timers
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so that we can observe the outputs of
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the two
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timers I am starting the pwm for the
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timer 2 first
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let's also give some delay between them
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so if the slave mode doesn't work you
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can clearly see the timer 2's output
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before the timer
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one let's build and Flash the program to
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the
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board here I have connected the timer
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one to Channel Zero and Tim Tim 2's
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output to the channel
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one here you can see the output of both
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the timers let me reset the board to see
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what happens in the beginning here you
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can see the timer 2's output goes low
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but the pwm doesn't start actually pwm
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is working it's just that the counter
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was initialized to zero and it's not
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counting up the counter is blocked and
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this is why the pwm output is always Z Z
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now this is the part where the timer 1
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pwm starts its counter was also
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initialized with zero the counter counts
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up and overflows at this point once the
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counter overflows an update event is
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generated which triggers the counter of
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the timer 2 and the timer 2's counter
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starts
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counting finally you can see the pwm W
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form of the timer 2 so we can see how
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the timer 2's counter was blocked until
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the timer one generated an update event
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now let me quickly show the output of
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this same configuration without the
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slave mode being
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used you can see the rest of the
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configuration is the same we will keep
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the code unchanged let's just flash it
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to the
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board here you can see the output the
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timer 2os pwm actually started way
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before the timer one this is how we
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programmed our timers and without the
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slave mode triggering it shows the
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output in that way so we saw the effect
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of using the slave mode with trigger
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mode and how it delays the counter until
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the master generates an update
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event let's take this further and this
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time we will start three slave timers
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using the same
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Master as you can see in the picture the
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timers two three and four can be
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controlled by the master timer one using
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the same signal it R Zer we will simply
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set up the timers three and four just
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like we did for the timer two I am
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enabling the pwm for both of these
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timers
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that's it for the setup let's generate
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the code now in the main file we will
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start the pwm for all four
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timers I am starting the slave timers
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first each with the delay of 500
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milliseconds since the timers are
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working in the slave mode all three of
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them will start at the same time after
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the Overflow occurs in the timer one
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let's build and Flash the code I forgot
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to change the channel polarity for the
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timer 3 and four let me do that
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quickly here you can see all three time
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timers have been enabled but their
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counter was
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blocked when the Overflow occurred in
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the timer one an update event was
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generated and all the three timers
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started counting up you can think of
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this as the parallel synchronization of
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the
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timers we can also synchronize them in
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series if you take a look at the table
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you can see here that the timer 3 can be
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controlled by the timer 2 using the it1
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signal and timer 4 can be controlled by
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the timer 3 using the it2 signal so in
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the timer 2 setup we will enable the
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trigger event as the update event now
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for timer 3 change the trigger source to
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it
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R1 also enable the trigger event for the
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timer 3 changed the trigger source for
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timer 4 to it
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R2 we have cascaded them in the ser
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series and the next timer will only
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start once the previous timer has
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generated the update event the code will
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remain the same let's build and Flash it
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to the
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board all right we can clearly see a
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little different output than the
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previous case here is the Overflow of
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the timer one and timer 2 starts
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counting after that this is where the
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timer 2 overflows and timer three starts
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after that again timer 4 starts after
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the Overflow in the timer three keeping
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the channel polarity low is not giving a
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clear picture about this let me change
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the polarity to high and we will see the
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output again
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now you can visualize it in a better way
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now that we have the proper polarity let
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me explain how the pwm signal is
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generated I have already explained it in
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the previous tutorial about pwm but I am
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explaining again here we have the auto
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reload value and the pulse which is all
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also a capture compare value basically
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the counter counts up until it reaches
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the capture compare value the output
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remains high and after the capture
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compare value the output remains low
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till it reaches the auto reload value
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this is where the Overflow occurs and
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the counter reset back to
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zero zero marker is where the Overflow
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occurs in the timer one timer 2 starts
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after this moment and Marker 1 indicates
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the point where the Overflow occurs in
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the timer 2 marker 2 indicates the point
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where the Overflow occurs in the timer
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three you can see the timer three and
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four basically have the same wave form
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even as for the timing this is because
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both of these timers are running at 50%
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duty cycle so when the Overflow occurs
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for timer three the counter resets to
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zero this is the point where the update
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event is generated and the timer 4 also
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starts counting up both timers will
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count up at the same speed and hence you
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can see the same
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waveform I hope you understood how the
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master timer can control the start of
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the slave
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timers we will continue this timer
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Series where we will cover different
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functionalities of Master and slave
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timers the next video will cover how to
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generate 3 pwm signals with 100 120°
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phase
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shift this is it for the
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video you can download the code from the
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link in the
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description leave comments in case of
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any doubt keep watching and have a nice
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day ahead
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[Music]
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