35. OCR A Level (H446) SLR7 – 1.2 Addressing memory

What does the opcode '0001' represent in the fictional processor's instruction set?

• Add operation

• Multiply operation

• Divide operation

• Subtract operation

Answer explanation

The opcode '0001' represents the Add operation in the fictional processor's instruction set, making it the correct choice.

In immediate addressing, what does the instruction 'add 10' mean?

• Add the value 10 to the accumulator

• Add the value at memory address 10 to the accumulator

• Add the value at the address contained in memory address 10 to the accumulator

• Find the value at memory address 10 and add 10 to it

Answer explanation

Immediate addressing means directly using the value provided in the instruction, so 'add 10' means adding the value 10 to the accumulator.

What is the result of direct addressing with the instruction 'add 10'?

• Add the value found at the address contained in memory address 10

• Increment the value at memory address 10

• Go to memory address 10 and add that value to the accumulator

• Add 10 directly to the accumulator

Answer explanation

The result of direct addressing with the instruction 'add 10' is to go to memory address 10 and add that value to the accumulator.

In indirect addressing, what does 'add 10' instruct the computer to do?

• Find the address contained at memory address 10, then add the value found at this new address to the accumulator

• Add the value at memory address 10 to the accumulator

• Add the value of the index register to 10, then add this sum to the accumulator

• Add 10 to the accumulator

Answer explanation

In indirect addressing, 'add 10' instructs the computer to find the address contained at memory address 10, then add the value found at this new address to the accumulator.

How does indexed addressing work with the instruction 'add 10'?

• Add 10 to the accumulator

• Go to memory address 10 and add that value to the accumulator

• Add the value at the address obtained by adding 10 to the index register's value

• Multiply the value at memory address 10 by the index register's value

Answer explanation

Indexed addressing works by adding the value at the address obtained by adding 10 to the index register's value.

What is the maximum number of unique memory locations that can be addressed with a 4-bit operand?

• 16

• 256

• 64

• 128

Answer explanation

The maximum number of unique memory locations that can be addressed with a 4-bit operand is 16, as 2^4 equals 16.

What does the instruction 'lda 8' mean in immediate addressing mode?

• Add 8 to the accumulator

• Load the value found at the address contained in memory address 8

• Load the value at memory address 8 into the accumulator

• Load 8 into the accumulator

Answer explanation

The instruction 'lda 8' in immediate addressing mode means to load the value 8 into the accumulator, not the value found at memory address 8.

What value is loaded into the accumulator with 'lda 8' in direct addressing mode?

• 23

• 8

• 5

• 0

Answer explanation

The value loaded into the accumulator with 'lda 8' in direct addressing mode is 5, not 8. The number after 'lda' is the memory address, not the actual value to be loaded.

Using indirect addressing, what value does 'lda 8' load into the accumulator?

• 5

• 23

• 0

• 8

Answer explanation

Using indirect addressing, 'lda 8' loads the value stored at memory address 8 into the accumulator. Since the correct answer is '0', the value loaded into the accumulator would be '0'.

What value is loaded into the accumulator with 'lda 8' in indexed addressing mode?

• 8

• 23

• 5

• 0

Answer explanation

The value loaded into the accumulator with 'lda 8' in indexed addressing mode is 23, not 8. Therefore, the correct choice is 23.