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I2C Communication in STM32 (PART1) | Register Programming Explained #4
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Oct 11, 2020
Learn how to configure I2C on STM32 microcontrollers using **register-level programming** ā without HAL or LL drivers. This video walks through every step to set up the I2C interface manually using STM32 registers, including GPIO configuration, timing registers, and communication with the **MPU6050 sensor**. You'll learn how to: * Enable I2C clocks and GPIOs * Configure I2C pins for alternate function * Set I2C speed using `CCR` and `TRISE` * Generate I2C start/stop conditions * Write and read bytes using registers * Interface the MPU6050 sensor with STM32 š„ **Download Code + Files** š (https://controllerstech.com/stm32-i2c-configuration-using-registers/) šŗ **Related Videos**: * How to Receive Data using I2C * [STM32 Register Programming Playlist](https://www.youtube.com/playlist?list=PLfIJKC1ud8ghc4eFhI84z_3p3Ap2MCMV-) * MPU6050 with STM32 using HAL I have tested the code for LCD 16x2, and it works pretty well. For those who want use it :::: https://github.com/controllerstech/STM32/tree/master/LCD1602_I2C_NOHAL
View Video Transcript
0:10
[Music]
0:18
hello everyone
0:20
welcome to controllers tech this is the
0:23
fourth video in the register programming
0:26
and today we will see how can we use i2c
0:29
with stm32
0:30
using registers obviously
0:34
i am not going to use any hall related
0:36
code here
0:37
and there is a lot of registers to cover
0:39
so this video will be a bit longer
0:42
let's start by creating the project in
0:44
kyle id
0:47
create the project folder and give some
0:49
name to the project
0:53
[Music]
0:57
now choose the mcu here i am only going
1:00
to add the core
1:02
and device startup files
1:06
[Music]
1:07
here is our project now let's add the
1:11
main file
1:12
first i am going to add a main function
1:15
and a while loop inside it
1:27
let's add some basic library files
1:30
these are basically the clock
1:32
configuration and the timer
1:34
configuration files
1:36
i have already covered them in the first
1:38
two videos
1:47
let's include them in kyle also
2:02
[Music]
2:04
include the header files in the main
2:06
file
2:13
this is it for basic setup now
2:17
let's write a function to configure the
2:19
i2c
2:21
before we go any further let's check the
2:23
reference manual first
2:25
[Music]
2:32
this video will only cover the master
2:34
mode so let's check it out
2:38
here are the steps given to configure
2:40
the i2c
2:41
in the master mode we need to set the
2:44
input clock in the cr2 register
2:47
configure the clock control register
2:51
configure the rise time register
2:54
and finally enable peripheral
2:57
then a start condition must be sent
3:04
then there is slave address transmission
3:07
and then the data transmission
3:09
we will cover them all one by one
3:13
we will start with the configuration
3:16
part
3:31
here are the steps that need to be
3:33
followed
3:34
i have added some more steps for clock
3:37
and gpio
3:38
configuration also
3:46
let's start by enabling the i2c and gpio
3:50
clocks
3:50
[Music]
3:54
to do so let's go to the rcc peripheral
3:57
clock enable register
4:04
here you see the i2c1 is the 21st bit
4:09
and to enable this clock we need to
4:11
write a 1 in the 21st position
4:21
[Music]
4:23
now the gpio clocks
4:26
i am using i2c1 and here are the sda
4:31
and sdl pins they are pb8
4:35
and pb9 so i need to enable the gp
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iob clock
4:49
which is located in our cca hb1enr
4:54
register so
4:56
let's write a one to the first bit to
4:58
enable the gpio b
5:00
clock
5:06
now we need to configure the pins
5:09
here first of all we will select the
5:12
alternate functions for the pins
5:15
this can be done in the modern register
5:19
as you know i am using pin number 8 and
5:22
9
5:22
so i need to write in mode 8 and mode 9
5:27
and to select alternate function i need
5:29
to write a 1 and a 0
5:32
which is basically writing a 2 in the
5:34
16th
5:35
and the 18th position
5:38
[Music]
5:45
next we need to select the open drain
5:48
output in the o type register
5:54
[Music]
6:00
here we will just write a one in the
6:02
eighth and ninth bit
6:03
for the pin pb8 and pb9
6:11
[Music]
6:15
next select the high speed for the pins
6:22
again we need to write a 3 in the 16th
6:25
and 18th position
6:39
[Music]
6:41
next select the pull-up for both the
6:44
[Music]
6:46
pins
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in the pupdr register i need to write a
6:53
1
6:54
again in the 16th and 18th position
7:02
[Music]
7:12
and now finally we will configure the
7:15
alternate functions
7:23
this can be done in the afr register but
7:26
before that
7:26
we need to see what values we are going
7:28
to use
7:36
as you can see here afrl register is
7:39
used for pins 0 to 7
7:41
and if you are using pins 8 to 15 you
7:44
need to use
7:45
a frh register
7:48
as i am using i2c1 i need to select
7:51
af4 let's go back to afrh register
8:03
here i need to write a 4 to the pins 8
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and
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9 which is basically the 0th and the 4th
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bits
8:21
here afr1 means the afrh register and in
8:26
case of aflo register
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use afr0 that's all for the pins
8:32
configuration
8:34
now let's start the i2c part
8:37
first of all we will reset the i2c
8:41
this can be useful in re-initializing
8:43
the peripheral after the error
8:45
or any locked state
8:51
15th bit of cr1 register can be used
8:54
for his purpose
8:59
[Music]
9:04
so we will first put the i2c in the
9:06
reset state
9:07
and then take it out of the reset
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after the reset state we need to program
9:14
the peripheral input clock in the cr2
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register
9:21
so what is the peripheral input clock
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here
9:25
let's see the data sheet to understand
9:34
that
9:39
as you can see here the i2c1 is
9:42
connected to the apb1
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which can run at 45 megahertz
9:51
and this is the clock setup that i am
9:53
using right now
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as i have shown in my first video
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the apb1 clock is running at 45
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megahertz
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and that's my peripheral input clock for
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the i2c1
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here is the cr2 register and the first
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five bytes are used for frequency
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the maximum value can be 50 megahertz
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and minimum
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as 2 megahertz these values are anyway
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in megahertz
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and so i just need to input 45 here
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[Music]
10:49
now the clock control register pay
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attention here
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as this will involve some calculations
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[Music]
11:10
here i am going to select the standard
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mode so 15th bit will be zero
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[Music]
11:19
duty will also be zero as i am not using
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the fast mode
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and now the ccr value
11:28
in standard mode we can calculate ccr by
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either using the t
11:32
high formula or t low formula
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i am going to use t high here
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as you can see the t high is equal to
11:47
the rise time for clock plus the clock
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high duration
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and these values can be found in the
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data sheet
11:59
so basically the formula for ccr will
12:02
become like this
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go to the i2c characteristics in the
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data sheet
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and here you can find all the values for
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your device
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i have the clock rise time of 1000
12:28
nanoseconds
12:30
and clock high time of 4 microseconds
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which is 4 000
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nanoseconds
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also time for pcl k1 can be found by 1
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divide by the clock frequency
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and finally the ccr value is 225
12:54
let's write 225 to the ccr
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register
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next is the calculation for the t rise
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you can read the details here on the
13:18
reference manual
13:30
but basically it comes to this formula
13:33
and we got the t
13:34
rise as 46.
13:36
[Music]
13:44
let's update it
13:52
now we need to enable the i2c peripheral
14:06
we can do that by setting the bit zero
14:09
of the cr1 register
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please note that this here should be bit
14:17
0
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not 1. this is all for the configuration
14:23
now let's write a function for i2c start
14:32
[Music]
14:34
here we first set the start bit and then
14:36
wait for the sb bit to set
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this basically indicates that the start
14:42
condition is generated
14:46
[Music]
14:48
let's see the registers start bit is bit
14:52
8 of the cr1 register
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[Music]
15:00
so write a one to the eighth bit
15:12
[Music]
15:16
sb is the bit zero in the status
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register one
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and if it is set it means that the start
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condition generated
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so we will wait for the bit 0 to set in
15:28
the sr1 register
15:30
[Music]
15:36
now let's write a function for writing
15:38
the data to the i2c
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device
15:54
[Music]
15:57
the description is given here but you
15:59
will better understand it with this
16:01
figure here
16:06
so before writing the data we must check
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for this particular event
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which says that the txe bit must be 1 to
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indicate that the buffer is empty
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then we write the data and after we are
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finished writing
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we check for event ev8 which says that
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the txe
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and btf bits must be one to indicate the
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transfer has finished
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[Music]
16:35
so we will wait for the txe bit to set
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then send the data
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and then wait for btf bit to set
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in the status register 1 bit 2 is the
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btf bit
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and bit 7 is the txe bit
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let's first wait for the txe bit to set
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then load the data into the data
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register
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and wait for byte transfer to finish
17:50
next another function for sending the
17:53
slave address
17:59
let's see the steps again
18:11
here after sending the slave address the
18:14
addr bit will be set to indicate that
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the transfer is finished
18:19
and then we need to read the sr1 and sr2
18:22
registers to clear the addr bit
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addr is the bit 1 in the status register
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1.
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so here are the steps need to be
18:48
followed
18:50
first send the address into the data
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register
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now wait for the addr bit to set
19:01
and then just read the sr1 and sr2
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registers to clear the addr bit
19:11
[Music]
19:12
and finally a function to stop the i2c
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[Music]
19:31
[Music]
19:32
ninth bit of the cr1 register is the
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stop bit
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and we will write a one to the ninth bit
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in order to stop the i2c
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this is basically all but i just want to
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add one more function here
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i2c write multi can be used when we want
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to write more than one byte of data at a
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time
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here i am passing the size as the
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parameter which is the number of bytes
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we want to write
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we need to follow the same steps that we
20:05
did in the right function
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but with little changes of course
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let's take a look at that figure again
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as you see here we can send multiple
20:20
data bytes
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but before sending the next data byte we
20:23
must perform the check for event eight
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that means we must wait for the txe bit
20:29
to set
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and after sending the last data byte we
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will wait for the btf bit to set
20:35
[Music]
20:44
here first check if the txe bit
20:48
is set and before sending data
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we need to perform the same check every
20:55
[Music]
21:00
time
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[Music]
21:05
once the last data byte is sent wait for
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the btf bit to set
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that's all for the i2c setup
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now let's see some working
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first of all i will include the sysclock
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config and
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timer configures usual
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include the i2c config also
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before going any forward let's see what
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device i have
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here i have is apcf 8574
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which is used to drive the lcd displays
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you can see the input pins right here we
21:47
have clock and data pins for the i2c
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[Music]
21:56
if you google the pin out for this
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module you can see how the pins are
22:00
actually connected
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the numbering on the lcd here is exactly
22:05
the same as it is on the module
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so we have the fourth pin connected to
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p0 5 to p1
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6 to p2 and then from 11 to 14 are
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connected to the p4 to p7
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so here i cannot control the first three
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pins of this module
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fourth pin is p0 p1 p2
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and then p4 to p7 also
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i have some leds here and i will attach
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them to this module
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notice here that i have first led
23:02
connected to p0
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second to p1 then this one is p4
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p5 p6 and p7
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now connect the vcc to 5 volts
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ground to ground clock to clock and data
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to data
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let's send the start condition first
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we need the address of the slave here
23:38
let's check the data sheet of the module
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[Music]
23:49
in my case pin a0 a1
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and a2 are high so the address will be 0
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cross
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4 e these pins are high by default
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and if you have more than one module
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attached to the same i2c
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pins you can ground these pins to change
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the address accordingly
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[Music]
24:12
as you can see the sequence here we send
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the start first
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then send the address then send the data
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and finally stop
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[Music]
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let's send the address 0 cross 4 e
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i am going to write 0 cross 0 1 that
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means i am setting the pin
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p 0 only and send the stop
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let's build it
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go to options and type in the frequency
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here
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[Music]
24:55
select the st link
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and check reset and run let's flash it
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[Music]
25:12
you can see only the first led is on
25:16
so the code is working as expected
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let's try to switch the led zero cross
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zero two means
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only the second led should be on
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as expected it works i don't have the
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led three and four
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so i will turn on the fifth one
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for that i will send zero cross one zero
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i can turn on all of them by writing 0
25:48
cross ff
25:58
things are working just fine here
26:01
let's try to have some more fun with it
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i will put this in the while loop where
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i will turn on one led at a time with a
26:12
delay of 300 milliseconds
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[Music]
26:30
so it's working fine but there is gap of
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two leds
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and you can see it
26:41
let's try to modify the code a little
27:09
and now we don't have any gap between
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the leds
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you can change delay here to make it
27:16
look a bit better
27:22
great it looks awesome now
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this is it for this video you can
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download the code from the link in the
27:34
description
27:36
leave comments in case of any doubt
27:39
you can mail me if you have any
27:41
suggestions
27:43
keep watching be safe and have a nice
27:46
day ahead
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