Lecture 2

Question 1

Describe the hardware interrupts

Answer 1

The hardware interrupt occurs by the interrupt request signal from peripheral circuits.
The hardware interrupts has an external interrupt and internal interrupts

Question 2

Describe the software interrrupts

Answer 2

the software interrupt occurs by executing a dedicated instruction.

Question 3

What is the main difference between maskable and non maskable interrupt

Answer 3

Maskable interrupt is a hardware interrupt that can be disabled or ignored by the instructions of CPU
While;
A non-maskable interrupt is a hardware interrupt that cannot be disabled or ignored by the instructions of CPU.

Question 4

Mention other comparisions between maskable and non maskable interrupts

Answer 4

1. NMI cannot be masked off or made pending while MI can be masked off or made pending
2. NMI disables all maskable interrupts while MI does not disables all non maskable interrupts
3. NMI is used or emergency purposes like power failure or smoke detector while the MI is used to interface peripherals
4. NMI has higher priority while MI has lower prority
5. NMI is vectored while MI is vectored or non vectored
6. NMI response time is low while MI response time is high

Question 5

What is a watchdog timer>

Answer 5

A watchdog timer (WDT) isa timer that monitors microcontroller unit (MCU) programs to see if they are out of control or have stopped operating.

Question 6

Describe instruction formats

Answer 6

Instruction formats provide computer guidelines to perform tasks. Basically instruction formats consist of two units of information.

The operations to be performed (such as ADD, LOAD, MOVE etc. ) and

the address of the operand (data that is to be operated upon).

OPERATION||OPERAND ADDRESS

Question 7

Mention the two enconding formats that are presents in most computer architectures

Answer 7

Fixed lenghts: very computer instruction is represented using the same number of bytes,
Variable Lenght format

Question 8

Mention the most common instructinon formats

Answer 8

Zero operand
OPCODE only

One operand (usually a memory address)
OPCODE + 1 Address

Two operands (usually registers, or one register and one memory address)
OPCODE + 2 Addresses

Three operands (usually registers, or combinations of registers and memory)
OPCODE + 3 Addresses

Question 9

define address modes

Answer 9

Addressing mode refers to the mechanism employed for specifying operands.

Question 10

Mention types of addressing modes

Answer 10

Direct
Indirect
Indexed
Relative
Intermediate

Question 11

Describe Direct

Answer 11

Only one memory reference is needed and the operand’s address is contained in the instruction.

Question 12

Describe Indirect

Answer 12

Two memory references are needed.

Question 13

Describe indexed

Answer 13

A constant is added to the contents of a register known as the index register in order to determine the operand’s address

Question 14

Describe relative

Answer 14

The program counter (PC) takes the place of the index register, otherwise it is identical to indexed addressing.

Question 15

Describe Immediate

Answer 15

The operand’s value is directly specified in the instruction itself.

Question 16

What is memory instruction

Answer 16

Memory instruction are set of instruction used to read from or write to memory

Question 17

Mention and describe

Answer 17

1 LOAD Fetch data from memory and loads to a register or memory
2 STORE Write data into memory from a register (memory location)
3 MOVE Transfer or copy data from one memory location to another
4 PUSH Store data from a register to stack
5 POP Retrieve data from stack into a register
6 COMPARE (CMP) Compare two values stored in a memory or register

Question 18

What are I/O instructions

Answer 18

They are used to transfer data between the computer and peripheral devices
The two basic I/O instructions used are the
INPUT and
OUTPUT instructions.

Question 19

Describe Common I/O instructions

Answer 19

1 INPUT Fetch data from memory and loads to a register or memory
2 OUTPUT Write data into memory from a register (memory location)
3 CONTROL (CTRL) Transfer or copy data from one memory location to another