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STM32 TIMERS #6. Timer Synchronization || 3 Phase PWM
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Jan 2, 2023
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View Video Transcript
0:00
foreign
0:01
[Music]
0:09
hello and welcome to controllers Tech
0:13
this is the sixth video in the SDM 32
0:16
timer series and today we will continue
0:18
with another application of the timer
0:20
synchronization
0:22
in the previous video we saw how the
0:24
master timer can control the start of
0:26
the counter of the slave timer by using
0:29
the slave mode along with the trigger
0:31
mode
0:32
there was however a restriction
0:35
the slave counter could start only when
0:37
the master counter overflows
0:40
today we will see how the master timer
0:42
can issue a trigger signal when it
0:44
reaches a predefined value and by making
0:46
use of this feature we will generate a
0:49
three-phase pwm signal
0:51
basically the signal will be generated
0:54
when the counter reaches 33 of its value
0:58
this is the point where the timer 2 will
1:00
start counting and it will also generate
1:03
a signal when it reaches 33 percent of
1:05
its value
1:07
then the timer 3 will start counting
1:10
since all the timers will have the same
1:13
frequency and Duty we will be able to
1:15
generate three pwm signals which will be
1:18
120 degrees out of phase with each other
1:22
here you can see the internal trigger
1:24
connection which you can find in the
1:26
reference Manual of your controller
1:29
this is the table for
1:31
f446re controller
1:34
you can see the timer 2 can be
1:36
controlled by timer 1 by using the itr0
1:39
signal
1:41
similarly the timer 3 can be controlled
1:44
by the timer 2 by using the itr1 signal
1:48
this table might be different for your
1:50
controller so you must look in the
1:52
reference Manual of your controller
1:55
this is the picture I took from one of
1:57
the STS videos
1:59
here you can see how this whole system
2:02
will work
2:03
basically the timer one will generate a
2:06
pwm signal and when the counter reaches
2:09
the 33 percent of its value its output
2:11
compare signal will go high
2:14
this is where the itr0 signal will be
2:17
issued and the timer 2 will start
2:19
counting from this point
2:22
when the timer 2's counter reaches 33 of
2:25
its value its output compare signal will
2:28
also go high
2:29
and this is the point where the timer 2
2:32
will generate the itr1 signal and the
2:35
timer 3 will start counting from this
2:37
point
2:38
let's start the cube IDE and create a
2:41
new project
2:45
I am using the nucleo
2:47
f446re controller
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give some name to the project and click
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finish
2:57
let's set up the clocks first
3:00
I am selecting the external Crystal to
3:02
provide the clock
3:04
the board has eight megahertz Crystal on
3:06
it and I want to run the system at 90
3:09
megahertz frequency
3:11
I am choosing 90 because that's the
3:14
maximum clock at which the APB one time
3:16
o'clock can run at
3:18
and I want both the APB buses to run at
3:21
the same frequency so that we could use
3:23
the same configuration for all three
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timers
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let's configure the timers now
3:29
timer 1 is going to be the master for
3:32
timer 2.
3:33
here we will generate the pwm signal on
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Channel 1.
3:38
also output compare with no output on
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channel 2 as this will be used for the
3:43
internal trigger
3:45
let's configure the pwm frequency and
3:48
duty cycle the timer is running at 90
3:51
megahertz so a prescaler of 90 will
3:54
bring down the frequency to 1 megahertz
3:57
then the auto reload of 10 000 will
4:00
further reduce the frequency to 100
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Hertz
4:03
now for the trigger event selection we
4:06
will go with the output compare for
4:08
Channel 2. this oc2 ref is used as the
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trigger signal and it will trigger the
4:14
timer too
4:15
here I am setting the pwm signal duty
4:18
cycle at 40 percent
4:22
for the output compare change the mode
4:24
to active level on Match
4:27
this will basically activate the signal
4:29
once the counter value matches the
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compare value
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and this compare value we will set it at
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33 of the auto reload value
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this is it for the timer one let's
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configure the timer 2 now
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timer 2 will act as a slave for timer 1
4:47
and master for timer 3. we will use the
4:51
trigger mode so that the counter starts
4:53
counting once the itr0 signal is
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received by the timer
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the rest of the configuration is exactly
5:00
the same as the timer 1.
5:02
so basically the timer 2 counter will
5:05
start upon receiving the signal from the
5:07
timer 1. once the counter reaches 33 of
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the auto reload value the output compare
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signal will go high which will generate
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the itr1 event
5:19
and now we will configure the time of 3
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which is a slave to the timer 2 and can
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be controlled by using the itr1 trigger
5:28
we don't need to generate the output
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compare for timer 3 and the rest of the
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configuration is the same as that of the
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other timers
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here these three pwm output pins are
5:39
connected to the logic analyzer
5:42
let's save the project to generate the
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code
5:50
there is not much in the coding part we
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just have to start the pwm for channel 1
5:55
and output compare for Channel 2.
6:14
we will only enable the pwm for timer 3
6:17
as we have not set the output compare
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for this
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that's it for the code part let's build
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and Flash it to the board
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I am using the logic analyzer to see the
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output of the pwm
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let me reset the board once
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we will start at the first Rising edge
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of the timer 1 output
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I am setting two more markers for the
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timer two and three
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now in the measurement set the first
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marker as the T 0.
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you can see the timestamps of the other
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markers compared to the first one
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note that all three pwm have the same
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frequency of 100 Hertz so the period is
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10 milliseconds
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now you can see the second pwm starts at
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3.3 milliseconds and the third one
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starts at 6.6 milliseconds
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if you convert this time to angles you
7:57
could observe the 120 degrees phase
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difference between these waves
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this phase difference will remain
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constant so if you add more markers
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anywhere on the waves you could still
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see the same time difference between
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them
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so we saw how to generate a three-phase
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pwm signal using the timer
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synchronization technique
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I hope you understood the process
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I will continue the timer series and in
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the next video we will see how to
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Cascade the timers so that we can make
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two 16-bit timers to behave as a single
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32-bit timer
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this is it for today
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the link to download the code is in the
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description below
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leave comments in case of any doubt keep
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watching and have a nice day ahead