In Ex $3\mathrm{.}1$ we are going to enable PORT B pin $5($PB$5)$ as an output,

which is connected to the DISP DP net. This net controls DS$1-$DP

which is an active$-$low device.

TASK: Write assembly code such that when we enable PB$5$ as an output,

DS$1-$DP is dim.

TIP: Use the predefined register names and bitmasks from avr$/$io$.$h to

write your code.

$*/$

$/**$ CODE: Write your code for Ex $3\mathrm{.}0$ above this line. $*/$

$/**$ Ex $3\mathrm{.}1$

TASK: Write assembly code to enable the pin connected to the DISP DP

net as an output.

$*/$

$/**$ CODE: Write your code for Ex $3\mathrm{.}1$ above this line. $*/$

$/**$ EX: $3\mathrm{.}2$

In later exercises you will be required to read the state of

pushbuttons S$1$ and S$4.$

TASK: Write assembly code to enable the internal pull$-$up resistors

for the pins connected to these pushbuttons.

$*/$

$/**$ CODE: Write your code for Ex $3\mathrm{.}2$ above this line. $*/$

$/**$ EX: $3\mathrm{.}3$

TASK: Write assembly code to illuminate DS$1-$DP$.$

$*/$

$/**$ CODE: Write your code for Ex $3\mathrm{.}3$ above this line. $*/$

$//$ The code between the "loop$\_100$ms$"$ and "end$\_$loop$\_100$ms$"$ labels will

$//$ execute approximately $10$ times per second.

loop$\_100$ms:

$/**$ EX: $3\mathrm{.}4$

TASK: Write assembly code to read the state of the BUTTON$0$ net and

store one of two distinct values in register R$17.$

$-$ If S$1$ is pressed, R$17$ should contain zero as this net will be

connected to ground.

$-$ If S$1$ is released, R$17$ should contain a non$-$zero value as the

internal pull$-$up resistor will pull the net to $3\mathrm{.}3$ V$.$

HINT: Use the IN register to read the state of the entire pinset on

PORTA, and then use a bitmask and bitwise operation to isolate only

the bit corresponding to the pin connected to the BUTTON$0$ net.

$*/$

$/**$ CODE: Write your code for Ex $3\mathrm{.}4$ above this line. $*/$

$/**$ EX: $3\mathrm{.}5$

The two instructions below check the value in R$17$ to determine

whether S$1$ is pressed.

When S$1$ is released, the "brne" $($branch if not equal$)$ instruction

will succeed $($as R$17$ is not equal to $0).$ This will update the PC to

the location of the instruction which appears after $"$ex$35\_$end",

skipping any code between $"$ex$35\_$if$"$ and $"$ex$35\_$end".

TASK: Write assembly code to toggle the state of DS$1-$DP when S$1$ is

pressed.

$*/$

cpi r$17,0//$ Compare R$17$ with $0$

brne ex$35\_$end $//$ branch to $"$ex$35\_$end" if R$17!=0$

ex$35\_$if:

$/**$ CODE: Write your code for Ex $3\mathrm{.}5$ below this line. $*/$

$/**$ CODE: Write your code for Ex $3\mathrm{.}5$ above this line. $*/$

ex$35\_$end:

end$\_$loop$\_100$ms:

$//$ The code between the "loop$\_10$ms$"$ and "end$\_$loop$\_10$ms$"$ labels will

$//$ execute approximately $100$ times per second.

loop$\_10$ms:

$/**$ EX: $3\mathrm{.}6$

At the start of this program, some code was included to set up the

Timer Counter A $0($TCA$0)$ peripheral to synthesise a $200$ Hz waveform

to drive the piezo buzzer connected to the BUZZER net.

TCA$0$ will automatically override the output of the pin connected to

the BUZZER net, however, the pin needs to be configured as an output

for the waveform to define the state of the BUZZER net.

TASK: Write assembly code such that the buzzer is driven $($audible$),$

when S$4$ is pressed, and not driven $($silent$),$ when S$4$ is released.

HINT: The code to read the state of the BUTTON$3$ net should be

similar to what you wrote in Ex $3\mathrm{.}4.$

$*/$

$/**$ CODE: Write your code for Ex $3\mathrm{.}6$ below this line. $*/$

cpi r$18,0//$ Compare R$18$ with $0$

brne ex$36\_$else $//$ branch to $"$ex$36\_$else" if R$18!=0$

ex$36\_$if:

rjmp ex$36\_$end $//$ Ensure the program skips over the else block

ex$36\_$else: