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STM32 as I2C Slave || PART 2
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Jun 24, 2023
Purchase the Products shown in this video from :: https://controllerstech.store ________________________________________________________________________________________ STM32 I2C Slave PART1 :::: https://youtu.be/X7WZQka2FHQ STM32 I2C Slave PART3 :::: https://youtu.be/SfM2lGQKGOs I2C SLAVE Playlist :::: https://www.youtube.com/playlist?list=PLfIJKC1ud8gj_P7Qb28aTr0t92uk_vwg0 STM32 Playlist :::: https://www.youtube.com/playlist?list=PLfIJKC1ud8gga7xeUUJ-bRUbeChfTOOBd DOWNLOAD THIS PROJECT FROM :::: https://controllerstech.com/stm32-as-i2c-slave-part-2/ ________________________________________________________________________________________ ******* SUPPORT US BY DONATING****** https://paypal.me/controllertech *******Join the Membership******* https://www.youtube.com/channel/UCkdqtSMnhYuMsJkyHOxiPZQ/join
View Video Transcript
0:00
foreign
0:09
Tech
0:12
this is the second video in the i2c
0:14
slave series and today we will continue
0:17
from where we left in the previous video
0:20
we saw how to write a simple code for
0:22
the slave to receive the data in the
0:24
interrupt mode
0:26
if you remember we wrote the function to
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receive six bytes of data and set the
0:31
transfer option as the first and last
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frame
0:34
this enabled the slave to receive six
0:37
bytes of data and if the master sent
0:39
more than six bytes the slave sent the
0:42
neck response
0:43
I also mentioned that since the slave is
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set to receive six bytes if the master
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sends less than that the slave will
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generate an acknowledgment failure error
0:53
let's see it again
0:57
this is the previous project we worked
1:00
with
1:01
let me launch the debugger
1:11
all right it's ready now
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I am putting a break point in the error
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callback function
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let's send two bytes of data
1:24
I forgot to run the debugger
1:32
all right we have received the two bytes
1:35
and the breakpoint also got the hit
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this means indeed there is an error
1:41
if you hover on the i2c you can see the
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error code that is 4.
1:47
let's see the i2c header file to know
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what error is this
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here you can see the error 4 corresponds
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to the a-f error that is acknowledgment
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failure error
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if the master sends six bytes of data we
2:04
will not get any error because it is
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supposed to receive 6 bytes
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but sending less than that will trigger
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the a-f error
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this error Rises because the slave
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detects an early stop condition we will
2:18
talk about this in a while
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the AF error is not an issue here
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as long as we are receiving the data it
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should be fine
2:28
we can just clear the error and move on
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with receiving
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the problem with the previous code was
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that it only received a fixed amount of
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data
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if we are using this code for
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communication between two devices and we
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don't know how much data the master is
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going to send we can't use it there
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so today we will make changes to the
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code so that the slave can receive
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pretty much any amount of data without
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sending a knack response
2:57
in the previous video we used the
3:00
transfer option first and last frame
3:03
today we will check out other options we
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have like i2c first frame next frame and
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the last frame
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the first frame is used to manage the
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start condition and the data transfer is
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done without a final stop condition
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the next frame is used to manage a
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restart condition and the data transfer
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is done again without a final stop
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condition
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the last frame is again used to manage a
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restart condition but the data transfer
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is done with a final stop condition
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you see how these options are very
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similar yet different from each other
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basically the first frame is used when
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you want to receive data where the
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master is starting the communication
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the next and the last frame is used to
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receive data where the master is using a
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restart condition basically in a
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situation where it wants to switch to a
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read from right or vice versa
4:00
the last frame is used when the slave
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wants to end the transfer
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if we'll receive the data with the
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option of the last frame so as to
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indicate that it does not want to
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receive any more
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this certainly does not mean that the
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master will stop transmitting it's just
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that the master will send NAC after this
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let's see all of this in the operation
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now
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let's define some new variables first
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the RX count will be used to keep the
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track of the buffer position
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I am also defining different counters so
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that we know which function was called
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how many times
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when there is an address match this
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address callback is called
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here we will first increment the address
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counter and then the slave will receive
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one byte of data with the indication
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that it is the first frame
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once the slave successfully receives one
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bite the receive complete callback will
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be called
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here we will increment the RX count so
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that the new data can be saved at a new
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location in the buffer
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if the RX count exceeds the buffer size
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reset it back to zero so that it starts
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overwriting the data from the beginning
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this whole Arrangement will make this
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reception in a circular buffer mode
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now we will again receive one byte of
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data and store it in a new position in
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the buffer
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this time we will provide the option
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next frame indicating that the slave is
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ready to receive the next data byte also
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let's increment the RX complete counter
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I am incrementing the error counter in
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the error callback function
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all right everything is set now let's
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build and debug the code
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let me add the counters in the live
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expression
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everything is set now so let's send the
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two bytes of data first
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here we received the data in the first
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two bytes of the buffer
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notice that the address counter is 1
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that means the address callback was only
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called once whereas the received
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callback was called twice
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basically when the master initiates the
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transfer and there is an address match
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the address callback gets called
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here the slave requests one data byte
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unsuccessfully receiving it the receive
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complete callback is called and the
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receive counter increments
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the slave requests another data byte
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on receiving a second byte the receive
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complete callback is called again and
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the counter increments to 2.
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the slave requests another data byte but
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the master is only sending two bytes
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hence a sop condition is detected while
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the slave was waiting for the data
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this triggers the acknowledgment failure
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error and the error counter is
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incremented to 1. now if a master sends
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a new data it will store at an updated
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position in the buffer
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since it's a fresh new data where the
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master again starts with the address
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matching the address counter is
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incremented again
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let's send six bytes now
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it started from a new updated position
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and once the data exceeded the buffer it
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started overwriting the data from the
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beginning
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let's see it one more time
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you can see the 7 8 overwrites the 1 2.
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the error will always be there each time
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the master transmits something
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this is because the slave never sends a
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stop condition
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the error actually arrives because the
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stop F bit is set in the status register
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this happens because the slave detected
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a stop condition while it was waiting
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for new data to arrive
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any way we can ignore the error for now
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we will handle it in future videos
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so we are able to receive the data in a
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circular mode where the new data
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overwrites the old data in the buffer
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more importantly the slave can receive
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as much data the master can send
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this is it for this video
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I hope you understood the concept
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in the next video we will make this
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receiving a little more interesting more
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like an idol line interrupt case in you
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art
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we will also see the usage of the option
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i2c last frame
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that's it for today
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the link to download the code is in the
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description
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leave comments in case of any doubt
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keep watching and have a nice day ahead