Question

1. State the voltages you expect to appear on PORTB pins(7 to 0) in each of the following cases:

portb = 0x47;

portb = 47;

portb = 11b;

portb = 101;

portb= 0b01010101;

2. If a variable called my_counter is declared as follows:-

unsigned char my_counter;

• How many bytes of RAM will the variable occupy?

• What is the minimum and maximum values the variable could have?

3. A variable called count has the value 20. What value does it have after the following statement has been executed?

count = count >> 2;

4. There is a difference between logical operators(!, || , &&) and bitwise operators (~, |, &). What values does portb have after the following statements are executed.

portb = 0x01 || 0x06;

portb = 0x01 | 0x06;

Answer 1

Answer :-

portb = 0x47; i.e. in binary it is 0100_0111 hence pins 3, 4, 5 and 7 will have zero voltage and pins 0, 1, 2 and 6 will have voltage label as Vcc.

portb = 47; i.e. in binary it is 0010_1111 hence pins 4, 6 and 7 will have zero voltage and pins 0, 1, 2, 3 and 5 will have voltage label as Vcc.

portb = 11b; hence pins 0 and 1 will have Vcc and rest all pins have zero potential.

portb = 101;i.e. in binary it is 0110_0101 hence pins 1, 3, 4 and 7 will have zero voltage and pins 0, 2, 5 and 6 will have voltage label as Vcc.

portb= 0b01010101; pins 0, 2, 4 and 6 have Vcc and 1, 3, 5 and 7 will have zero voltage label.

2. If a variable called my_counter is declared as follows:- unsigned char my_counter;

• How many bytes of RAM will the variable occupy? unsigned char have one byte of memory.
• What is the minimum and maximum values the variable could have? minimum when all 8-bits are zero in one byte so minimum value is zero. Maximum when all 8-bits are 1 i.e. 1111_1111 in binary. Hence 255 in decimal.

3. A variable called count has the value 20. What value does it have after the following statement has been executed?

count = count >> 2; This operation on count will make count to be divisible by 2 as right shift operation is equivalent of divide by two. Thus count = 10.

4. There is a difference between logical operators(!, || , &&) and bitwise operators (~, |, &). What values does portb have after the following statements are executed.

portb = 0x01 || 0x06;

portb will have value equal to 0x01 since logical operator gives either 0 or 1. Here 0x01 and 0x06 are non-zero numbers, so logical operator will give 1, hence portb = 0x01.

portb = 0x01 | 0x06;

here bitwise ORed value of 0x01 and 0x06 will be stored in variable portb. 0x01 = 0000_0001 and 0x06 = 0000_0110. The bitwise ORed value is 0000_0111 i.e. 0x07 in hex, hence portb = 0x07.