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#3. How to Configure UART using REGISTERS || STM32F4
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Sep 20, 2020
Purchase the Products shown in this video from :: https://controllerstech.store ________________________________________________________________________________________ STM32 REGISTERS PART2 :::: https://youtu.be/iImNVKJCq4Q STM32 REGISTERS PART4 :::: https://youtu.be/usvAIEdp_I8 STM32 REGISTER Playlist :::: https://www.youtube.com/playlist?list=PLfIJKC1ud8ghc4eFhI84z_3p3Ap2MCMV- STM32 Playlist :::: https://www.youtube.com/playlist?list=PLfIJKC1ud8gga7xeUUJ-bRUbeChfTOOBd DOWNLOAD THIS PROJECT FROM :::: https://controllerstech.com/how-to-setup-uart-using-registers-in-stm32/ ________________________________________________________________________________________ ******* SUPPORT US BY DONATING****** https://paypal.me/controllertech *******Join the Membership******* https://www.youtube.com/channel/UCkdqtSMnhYuMsJkyHOxiPZQ/join
View Video Transcript
0:09
[Music]
0:16
hello everyone
0:18
welcome to controllers tech this is the
0:21
third video in the series of register
0:24
based programming for stm32
0:26
and today we will see how to use uart in
0:30
stm32
0:32
i will cover the basic sending and
0:34
receiving today
0:36
interrupts or dma will be covered later
0:41
let's start by creating the project in
0:43
kyle id
0:45
select the mcu here
0:53
i am only going to include the core and
0:55
the device
0:56
startup files
0:58
[Music]
1:07
first of all let's add a main file to
1:10
our project
1:12
[Music]
1:16
i will create a main function and a
1:19
while loop in it
1:29
next i am going to include the clock
1:32
configuration files
1:34
i have already covered this you can
1:36
check the first video in this playlist
1:44
[Music]
1:49
let's add those files in our project
1:56
[Music]
2:05
this configuration is to run my mcu at
2:07
maximum 180 megahertz clock frequency
2:23
let's include the rcc config.h in the
2:26
main
2:27
[Music]
2:33
some of you guys also requested me to
2:35
cover how to write the header files
2:38
and the source files well
2:41
i will also show that in this video
2:44
in my previous video i blinked the led
2:47
with the precise delay using the timer
2:50
this here is the main file from the code
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so i am going to use this file to write
2:57
a library for the delay
3:04
first create a new header file and let's
3:07
call it
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delay.h
3:09
[Music]
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header files basically contains the
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functions that you can use globally
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[Music]
3:27
so i am going to include these functions
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into the delay.h file
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so that later i will be able to call
3:34
them from the main file
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you see we have error with the integer
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types
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this is because we haven't included any
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references yet
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let's include std into.h and the error
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is gone
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now let's create a source file and call
3:52
it delay.c
3:59
[Music]
4:02
source file will contain the details
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about the functions
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let's include the delay.h here
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[Music]
4:12
i am also including the rcc config.h
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as it already contains the device header
4:18
files
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you can also include the device headers
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directly here
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we need the device headers because we
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are using the registers
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which are defined in the device header
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files
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that's all we have created the delay
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library
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now let's call the delay.h in the main
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file
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[Music]
4:53
let's build it once
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[Music]
4:59
we don't have any errors so we are good
5:02
to go
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now we will start with the uart
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configuration
5:10
let's take a look at the reference
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manual
5:29
[Music]
5:30
here is the procedure to configure the
5:32
uart
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so first we need to enable the uart
5:37
then define the word length
5:41
then select the board rate and so on
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here are the detailed steps that we need
5:54
to follow
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first of all we need to enable the
5:58
clocks
6:00
then configure the pins for alternate
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functions
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and then we will configure the uart as
6:06
per the reference manual
6:23
so let's start with the first step
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i am using uart too so the pins used up
6:37
in pa2
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and pin pa3
6:47
[Music]
6:54
to enable the clocks we will look into
6:56
the rcc
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registers
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rcc apb1 peripheral clock enable
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register
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as you can see here the 17th bit of this
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register
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enables the uart 2 clock
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let's write a 1 in the 17th position
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we also need to enable the gpio clock
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for the tx and rx
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pins this can be done in the ahb1 enable
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register
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[Music]
7:57
here zeroth bit controls the gpioa
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clock
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[Music]
8:07
let's write a one in the zeroth position
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to enable gpioa
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clock
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now configure the alternate function for
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the gpio
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[Music]
8:24
let's see the gpio registers
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[Music]
8:32
gpio mode register is used to set up
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different roles for the gpio pins
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and as you can see here we can set the
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alternate functions also
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i am using pins pa2 and pa3 for the
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transmission
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so i need to modify the mode r2 and mode
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are 3 registers
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basically i need to write a 2 in the 4th
9:00
and the 6th positions
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[Music]
9:05
writer 2 in the fourth position and
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right a two
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in the sixth position
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[Music]
9:38
next we need to configure the speed for
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these pins
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and we should select the highest
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possible speed
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so this time we need to write a 3 in the
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fourth
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and the 6th positions
10:20
[Music]
10:24
we don't need to set up any of these
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we will directly go to the alternate
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function registers
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[Music]
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there are two alternate function
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registers af low
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and af high they both have the same
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alternate functions defined
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[Music]
10:53
we will come back to these but first
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let's see
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what setup do we need for the uart
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[Music]
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as you can see here from uart 1 to 3
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i need to select af7
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[Music]
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also note that airflow is used to
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control the pins 0 to 7
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and afi is used to control pins 8 to 15.
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as i have pin 2 and 3 for the uart 2
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i need to select af7 in alternate
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function low register
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[Music]
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so i need to write 7 in the 8th and the
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12th positions
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[Music]
12:04
here a f 0 represents the alternate
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function low register
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and afr1 would represent alternate
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function high register
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[Music]
12:18
that's all the setup needed for the pins
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now let's see the uart configuration
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first of all we need to enable the uart
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let's see the uart registers now
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control register 1 have the 13th bit as
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the uart enable bit
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and we need to write a 1 here
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[Music]
13:00
let's first reset all
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now write a 1 in the 13th position to
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enable the uart
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[Music]
13:16
next we need to program the m bit to
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define the word length
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it's the 12th bit in the cr1 register
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and we will keep it zero to select eight
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data bits
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[Music]
13:42
this should be in here not the ore
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now comes the important part that is
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selecting the board rate
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[Music]
13:58
board rate register is divided into two
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sections mantissa
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and the fractional parts fractional part
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only have four bits
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so maximum value it can accommodate is
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15.
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mantissa on the other hand have 12 bits
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and can have larger values also
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there are some examples given in this
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manual and we will try to understand the
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setup using those examples
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here is formula to calculate the baud
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rate
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this over eight here means the over
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sampling and it should be kept zero for
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now
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we will try to understand the usart div
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values
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suppose the use active value is 25.62
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we need to multiply the 0.62 with 16 to
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get the fractional part of board rate
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register
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so here the fractional part becomes 10
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and mantissa is anyway equal to 25
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let's see one more example this time the
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fractional part is 15.85
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so nearest integer is 16.
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now remember that the fractional part
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only have four bits
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so the maximum value it can have is 15.
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and here we got 16 so this one is the
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carry
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and it will be added to the mantissa and
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the fraction will become
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zero this makes up mantissa's 51.
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i hope you understood the process for
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calculation here
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now let's do the calculation for our
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board rate
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the formula here requires the clock
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frequency
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this is the timer diagram of f4
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here you can see uart 2 is connected to
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apb1
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which is running at 45 megahertz
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i have already covered the clock section
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in my first video and there you saw that
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all the clocks are running at their
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maximum
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frequencies
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[Music]
16:34
so the uart two clock is also running at
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45 megahertz
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and i want the board rate of 11 5 200.
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so i got the use octave as 24.414063
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out of this let's first do the
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calculation for fractional part to check
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if we get some carry or not
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otherwise we need to add that carry to
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the mantissa
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multiply the decimal value with 16
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and i got 6.624
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the nearest integer is 7 in this case
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which i need to feed
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to the fractional part
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so i need to write a 7 in the zeroth
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position and
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24 in the fourth position
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[Music]
17:41
now the last step is to enable the
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transmitter and the receiver
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[Music]
17:56
this can be done again in the control
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register one
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[Music]
18:13
you can see here the bit2 enables the
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receiver
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and the bit 3 enables the transmitter
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this completes the configuration for the
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uart
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now let's write a function to send the
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character to the uart
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to do so we need to copy the data into
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the usart dr register
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and then wait for the tc bit to set
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transmission complete bit gets set once
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the data is transferred to the shift
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[Music]
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register
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you can see the steps are as per given
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in the reference manual
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[Music]
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let's copy the data into the data
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register first
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t c is the sixth bit of the status
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register
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which becomes one when the transmission
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is complete
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so we will wait until the tc is one
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let's test this much part of the code
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first
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in the main function we will call the
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system clock config first
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then i am going to call the timer config
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and at last uart config
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timer here is just to provide
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appropriate delay
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in the while loop i am going to send a g
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and this should happen every one second
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we don't have any errors so let's go
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ahead
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before flashing we need to go to options
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and change the mcu frequency here
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mine is running at 180 megahertz
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change to sd link debugger
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let's open the console note the settings
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are as per the configuration
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that is board rate is eleven five two
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hundred
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data length is eight and no parity
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let's upload the code you can see that
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the g
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is being transmitted every one second
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so things are all right till now
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let's proceed forward let's create a
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function
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to send the string
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now i am going to send the hello every
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one second
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[Music]
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let's build and upload this one also
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this is also working all right so the
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transmission part is pretty good
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let's try to receive data now
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[Music]
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you uart get char will be used to
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receive a character
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here first we will wait for the rxne bit
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to set
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which indicates that we have a data
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pending to be read
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now we will read the data from the data
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register
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you can see the rxne is the fifth bit in
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the status register
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we will wait for this bit to set
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[Music]
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and now read the data from the data
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register
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[Music]
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[Music]
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now in the while loop let's read the
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data and then send the data back to the
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uart
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[Music]
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let's test this now
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[Music]
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as you can see the hello got transmitted
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back to uart
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here pink color is the one i am sending
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and black is the one i am receiving
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[Music]
24:02
it works all right for some parts but
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this is not the solution to receive
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unknown data length
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as you can see here the d is missing
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from world
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this can happen as we can't do the
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sending and receiving at the same time
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in the blocking mode
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to handle these scenarios we need to use
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interrupts
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but you can receive data of whatever
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length you want and store that data into
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some buffer
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later process that data and do whatever
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you want with it
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so here both the transmission and
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reception works properly
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i will go back to transmitting some
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other string
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[Music]
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and it works as expected this is it for
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this video
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the clock setup and the timer setup
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videos can be found in this playlist
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you can download the code from the link
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in the description
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next video will cover the i2c
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keep watching be safe and have a nice
25:21
day ahead
25:30
you
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