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How to Interface RS485 Module with STM32
Sep 24, 2022
Learn how to interface an RS-485 module with STM32, including wiring, configuration, and code implementation. š Download project files & article: STM32 RS485 Communication ā https://controllerstech.com/rs485-module-and-stm32/ š STM32 UART Tutorials ā https://controllerstech.com/stm32-hal/uart-tutorials/ š STM32 Modbus Tutorials ā https://controllerstech.com/stm32-hal/modbus-tutorials/ š ControllersTech Home ā https://controllerstech.com/ š Subscribe for more STM32 & Modbus tutorials! š Like & share to help others. š” Share this Video for RS485 tips! #STM32 #RS485 #EmbeddedSystems #Microcontroller #UART #EmbeddedC #Electronics #IoT #Controllerstech #CommunicationProtocols ________________________________________________________________________________________ ******* SUPPORT US ******* š Donate: https://paypal.me/controllertech š Join Membership: https://www.youtube.com/channel/UCkdqtSMnhYuMsJkyHOxiPZQ/join š Connect: Facebook: https://www.facebook.com/controllerstech Telegram: https://t.me/controllerstechdiscuss
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0:00
foreign
0:01
[Music]
0:04
Tech
0:06
[Music]
0:12
if you are a subscriber to my channel
0:14
you might have already found out that
0:16
soon I am going to start the modbus rtu
0:19
video series
0:21
I have also created a playlist for the
0:23
same and here are some videos for you to
0:25
understand some Basics about the modbus
0:28
standard
0:29
these videos are from some other Creator
0:31
and it explains very well what the
0:33
modbus is and why it was developed in
0:36
the first place
0:37
if you are interested in modbus do check
0:40
out these videos and I am going to skip
0:43
the basic explanation about it
0:45
I am going to use the rs485 for the
0:48
modbus communication and this is why
0:51
today's video is kind of related to
0:53
modbus also
0:54
today we will see how to use the rs-485
0:58
to TTL converter with our
1:00
microcontroller
1:01
so what is this rs-485
1:04
to put it in simple words just like
1:07
rs232
1:09
rs-485 is a protocol for serial
1:12
communication
1:13
compared to rs-232 it is faster and can
1:17
be used for data transmission over
1:19
longer cable lengths and in noisy
1:21
environments
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since the stm32 microcontrollers do not
1:26
support the rs-485 communication we will
1:30
use the rs-485 to TTL converter
1:33
this converter uses the max 485 chip and
1:37
converts the TTL signals to rs-485 and
1:41
vice versa
1:43
the converter has pins A and B here a is
1:47
the non-inverting pin and B is the
1:49
inverting PIN say for example if the
1:52
chip is powered with 5 volts and we are
1:55
sending 0 cross 9 5 Via the uart
1:58
the max 485 chip will amplify each bit
2:02
and this is how the output on the pins A
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and B is going to look like
2:07
notice that pin a is a non-inverting pin
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so the signal on it is either zero or
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plus 5 volts
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on the other hand pin B is an inverting
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pin so the signal is either 0 or minus 5
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volts
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now when this data is received by
2:25
another module it will interpret a zero
2:27
or one based on these differences
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if the voltage difference is maximum
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between the pins it's a 1 and if the
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difference is zero the bit is also zero
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I hope you understood how communication
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works now let's talk about the
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connection
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this is how the connection looks overall
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I have two mcus which are connected via
2:51
the two rs-485 to TTL converters
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let's dig deep into this
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picture shows the pin out of the module
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on the right side we have the VCC ground
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pin a and pin B
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the pins A and B must be connected to
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the similar pins on the other module
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you can see the connections between the
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corresponding A and B pins
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I have already explained the purpose of
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these pins
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on the left side the pin Ro which stands
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for receiver output must be connected to
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the RX pin of the MCU
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the Pindi I driver input is connected to
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the TX pin of the MCU
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the pins are e and d e are connected
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together
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IE stands for receiver enable it enables
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the module to receive the data
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but this is a low enable that means we
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must pull the pin low in order to enable
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the receiver
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similarly d e which is driver enable
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enables the module to transmit the data
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since this is a high enable pin we must
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pull it high in order to enable the
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transmit mode
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so in order to transmit the data that a
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pin must be pulled High and the re pin
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also should be high
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similarly to receive the data the re pin
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must be pulled low and d e pin also
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should be low
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this is why both the pins are tied
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together so pulling either one of them
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will also pull another pin to the same
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state
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this is the connection between the MCU
4:35
and the module
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the RO pin is connected to the pier 10
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the uart 1 RX pin
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the DI pin is connected to the pa9 the
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uart1tx PIN
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and t e and r e are connected to the pin
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pa8 which we will set as the output
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later
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the connection will remain similar with
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the other MCU also
5:00
let's start the queue IDE and create a
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new project
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I am using the
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stm32f103 controller give some name to
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the project and click finish
5:13
first of all we will enable the external
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Crystal for the clock
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the board has eight megahertz Crystal on
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it and we will run it at maximum 72
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megahertz
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then go to sys debug and enable serial
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wire
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set the time-based source to systic also
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now go to connectivity uart one and
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enable the asynchronous mode
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you can see here the pins peer 10 and
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pa9 are enabled as the RX and TX pins
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let's keep the board rate at 11 5 200.
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we have 8-bit word length no parity and
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one stop bit
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let's go to the interrupt Tab and enable
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the uart interrupt
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we will use the interrupt to receive
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data from the module
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this is it for the uart now we will set
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the pin pa8 as the output pin
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this is where the r e and d e pins will
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be connected I am naming this pin as the
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TX enable pin
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click save to generate the code
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let's first create the TX and RX buffers
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inside the main function we will call
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the receive to idle function in
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interrupt mode
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if you have been watching this channel
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you know what this function does for the
6:45
rest of you guys I will leave the link
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to the video in the description below
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basically during receiving if the uart
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sees the line idle for some time it
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triggers the interrupt
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this interrupt eventually calls the RX
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event handler function
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we will copy this event handle in our
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main file and inside it we will restart
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the interrupt
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Hull disables the interrupt after one
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call so we need to enable it again
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now we need to send the data to the uart
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so that it can be transferred via the
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module
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let's first create an index variable
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we will continuously transfer the data
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in the while loop
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first we will copy this string to the TX
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data array
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this string will always have the updated
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value of the index variable
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then we will call the function send data
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to send this string to the uart
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we will Define this function later
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and this process will repeat every one
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second
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now let's define the send data function
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as I mentioned in the beginning the r e
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and d e pins set the module as receiver
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or transmitter
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before sending the data we need to set
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this module as a transmitter and to do
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that we have to pull the de pin as high
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so here first of all we will set the TX
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enable pin as high
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then we will transmit the data via the
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uart
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and again we will pull the pin low so as
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to enable the receiver mode
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basically the module is always in the
8:38
receiver mode because we don't know when
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the data might arrive
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just before we send the data we put it
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in the transmitter mode and after
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sending it goes back to the receiver
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mode again
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we need to include some header files for
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the S printf and the string length
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functions
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all right everything is fine now
8:59
I am using
9:01
f446re as the second controller which is
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connected to another module
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the code used is exactly similar to the
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first one
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here is the send data function
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in the first controller I am sending the
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string which starts with f 1 0 3.
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when the data is received by the second
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controller it will just modify the first
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four bytes to F 4 4 6 and send the same
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string back to the first controller
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since I want this second controller to
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only respond to the data sent by the
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first one this is why the transmission
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program is written in the Callback
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itself
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there is nothing inside the while loop
9:44
here
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the code is already loaded into the f446
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so we will just see the f103 debugger
9:53
all right let's test this now
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both the controllers are connected to
10:05
the same computer so I am fixing the St
10:08
link to this configuration
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here I have put both the buffers in the
10:18
live expression let's put a break point
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at the send data function
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here you can see the data stored in the
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TX buffer and now this data will be sent
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to the module
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let's put another breakpoint in the
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Callback function
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it didn't hit the breakpoint but it's
10:40
fine here you can see the data received
10:45
we have some garbage characters also but
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this is because I didn't reset the f446
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and it already had the data in the RX
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buffer
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just ignore it for now
10:56
the data is exactly what we sent but the
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103 has been replaced with four four six
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we have hit the breakpoint this time but
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the received data is the same
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let me try again
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seems like the received data is not
11:18
updating
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maybe because of the breakpoints
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let's remove them and run the code
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freely
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all right now you can see the received
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data is exactly the same that we are
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sending except for the first few bytes
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anyway you can clear the buffer in the
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second controller after sending the data
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that way it will not send the extra
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characters
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that's all for this video
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in the next video we will start with the
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modbus and obviously we will use this
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rs485 module with it
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we will use stm32 as the master and read
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some holding and input registers of the
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slave
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the purpose of this video was just to
12:01
give an idea about how this rs-485 to
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TTL module actually works
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I hope everything was clear
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you can download the code from the link
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in the description
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keep watching and have a nice day ahead
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thank you foreign
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[Music]
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