Revision Lecture

Question 1

How do you create binary numbers?

Answer 1

0b
0B
B

Question 2

How do you create Hexadecimal numbers?

Answer 2

0x
0X

Question 3

For the DDRx, what is an input and what is an output?

Answer 3

0 = Input
1 = Output

Question 4

How can I make all pins on port A into input pins?

Answer 4

DDRA = 0b00000000

Question 5

How can I make the 4 lower bits of port B an output and the 4 higher bits into inputs?

Answer 5

DDRB = 0b00001111

Question 6

DDRA = 0x00; //Set port A as input
x = PINA;

What does the second line do?

Answer 6

//Read contents of port A

Question 7

What can PORTx - Port x Data Register do?

Answer 7

• Output data
• Activate / Deactive Pull Up Resistors

Question 8

How can I output 0xFF on Port B?

Answer 8

DDRB = 0b11111111; //Set all pins of port B as outputs
PORTB = 0xFF; //Write data on port

Question 9

How can I output data in variable x on port A?

Answer 9

DDRA = 0xFF; //Make port A an output
PORTA = x; //Output variable on port

Question 10

What is Aliasing?

Answer 10

Two or more signals have the same sampled representation

Question 11

What is the ADC resolution of an analog signal with a maximum value of 3.3V with a 10-bit ADC?

Answer 11

2^10 = 1024
3.3/1024 = 3.22mV

Question 12

What is the ADC frequency formula?

Answer 12

Frequency of CPU / Prescaler value

Question 13

What are the available ADC Prescaler Values?

Answer 13

2, 4, 8, 16, 32, 64, 128

Question 14

If I have a CPU frequency of 16MHz and use a prescaler of 64, what is the effective frequency?

Answer 14

16MHz / 64 = 250kHz

Question 15

What is the global interrupt bit?

Answer 15

sei()
cli()

Question 16

What is an ISR?

Answer 16

Interrupt Service Routine

Question 17

How do you write code for an ISR?

Answer 17

ISR(INT_vect)
{
}

Question 18

What are the rules for writing an Interrupt Service Routine?

Answer 18

• Keep it short
• Don’t use delay(), serial prints
• No input variables or returned variables
• All changes have to be made on global variables
• Shared variables should be declared volatile

Question 19

How do the ATmega2560 External Interrupts work?

Answer 19

INT7:0
Reset Pin = Pin30
PCINT23:0: Pin Change Interrupt

Question 20

How many steps are in an 8 bit timer?

Answer 20

256 steps
0 to 255

Question 21

What are the prescaler values available for a clock?

Answer 21

8, 64, 256, 1024

Question 22

How many timers are in the Atmega2560 and how many bits do they have?

Answer 22

Timer/Counter 0, 2: 8 bit
Timer/Counter 1, 3, 4, 5: 16 bit

Question 23

ISR(TIMER0_OVF_vect) //TIMER0 overflow interrupt service routine.
//This ISR is called automatically whenever TCNT0 overflows
{tot_overflow++; //Count the number of...
}
int main(void)
{ DDRL |= (1 << PL0); //connect LED to PL0
timer0_init(); //initialise Timer0
while (1)
{ if (tot_overflow >= 12) // Check if...
{ if (TCNT0 >= 53) // Check if...
{ PORTL ^= (1 << PL0); // toggles the led
TCNT0 = 0; // Reset the...
tot_overflow = 0; // Reset the...
}
}
}
}

Finish the comments

Answer 23

ISR(TIMER0_OVF_vect) //TIMER0 overflow interrupt service routine.
//This ISR is called automatically whenever TCNT0 overflows
{tot_overflow++; // count the number of overflows
}
int main(void)
{ DDRL |= (1 << PL0); //connect LED to PL0
timer0_init(); //initialise Timer0
while (1)
{ if (tot_overflow >= 12) // check if no. of overflows = 12
{ if (TCNT0 >= 53) // check if the timer count reaches 53
{ PORTL ^= (1 << PL0); // toggles the led
TCNT0 = 0; // reset the counter
tot_overflow = 0; // reset the overflow counter
}
}
}
}