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hello and welcome to controllers Tech
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this is the sixth video in the AVR
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series with explained mini development
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board from microchip and today we will
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continue with where we left in the
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previous one we will continue with the
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i2c master series and connect and
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control an actual slave device to the
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bus I am going to use the pcf8574 as the
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slave device which will receive the data
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from the MCU and will control some LEDs
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output let's check the data sheet of the
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device this is basically a 8bit IO
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expander for the i2c bus we will only
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cover the important details in this data
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sheet it supports the standard i2c
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communication with 100 khz frequency
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here is the block diagram of the device
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it has the three input pins a0 to A2
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which can be used to modify the address
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device we have the clock and data pins
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which will connect to the respective
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MCU there are eight outputs available on
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this device where we will connect the
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LEDs to here is the address of the
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device the 7bit slave address has the
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four fixed bits and the bits a0 to A2
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can be modified to modify the slave
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address here you can see the seven bit
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address for different
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bits the PCF module has all three bits
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connected to the vdd by default so the
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default address is 27
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hex here is the connection of the module
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pcf8574 module is generally used to
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connect to the LCD and therefore change
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changes the pin requirement from 16 pins
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pins as I mentioned the pins a 0 to A2
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are connected to the vdd by default and
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beside them is the connection to the
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ground the address can be modified by
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connecting the respective to the
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ground here you can see the output pins
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P2 we do not have access to the pin
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P3 then we have the pins P4 to p7
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I have connected the LEDs to all the
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pins which then connects to a common
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resistance the data and clock pins are
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connected to the pin pa1 and pa2
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respectively for the device to work
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properly both the pins must be pulled up
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to the VCC with 4.7 kiloohms
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resistance the module is powered with 5
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we will continue with the previous
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project last time we commented out the
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part where the master waits for the
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acknowledgement from the slave
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device since we have an actual slave
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device this time let's include it
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now also this statement was wrong as we
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need to check for the RX acknowledgement
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bit so the master sends the slave
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address to the bus when the address
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matches with a slave device it sends an
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response on receiving the
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acknowledgement the master continues to
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send data once all the data is
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transmitted the master sends the stock
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condition and returns
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zero if the slave does not acknowledge
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the address the master sends the stock
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condition and returns one let's write
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the main file now we need to control the
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LEDs connected to the pins shown in this
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connection diagram to turn the LED on we
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will simply write a one to the
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respective pin let's define an array to
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store the data for the
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LEDs these btes will set the respective
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pin high in the output of the slave
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device we have the bite for the p 0 P1
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P2 P4 P5 P6 and p7 the i2c is
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initialized in the main function in the
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while loop we will send one bite at a
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time so let's send the data in the F
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Loop the slave address is 27 hex and we
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will send one bite of the array at a
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time let's build the code
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now there are no errors so let's put a
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break point to this statement and debug
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we have hit the brake point you can
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check the LEDs connected to the module
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right now all the LEDs are off let's run
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the debugger now we hit the breake point
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again and the first led is on now the
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on all the LEDs are turning on one at a
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let's remove the break point and let the
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code run freely you can see the LEDs are
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turning on after a delay of 1 second let
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me change the delay to 100 milliseconds
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code you can see the result of 100
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milliseconds delay we will also see the
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output on the logic analyzer so let me
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change back the delay to 1 second and
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again the data is being transmitted
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every 1 second let's check one of these
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frames here the master sends the St
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condition and then the address 27 hex
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with the right bit the slave
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acknowledges the address and we can see
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the AK response on the bus the master
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then sends the data one hex and the
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slave acknowledges the data received
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then the master sends the stop condition
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after one second the master again sends
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the start followed by the slave address
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and a new data to write so I i2c master
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is working fine so far I will continue
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with it and in the next video we will
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see how to interface the LCD display via
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i2c after that we will also write the
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functions to receive the data from the
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device this is it for this video I hope
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you understood how to communicate to a
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slave device using the
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i2c you can download the code from the
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link in the description leave comments
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keep watching and have a nice day ahead
