Computer Architecture: Stack Pointer and Instructions

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Questions and Answers

Which pins correspond to the external hardware interrupts of the 8051?

P3.2 and P3.3 (correct)

P3.0 and P3.1

P3.0 and P3.2

P3.1 and P3.2

What priority level does a priority bit of 1 assign?

Medium priority

Low priority

High priority (correct)

No priority

What is the default mode of the external hardware interrupts upon reset of the 8051?

Level triggered (correct)

Edge triggered

Disabled mode

Both modes are enabled

What happens if the low-level interrupt signal is not removed before the ISR is finished?

Another interrupt is generated Signup and view all the answers

How often does the microcontroller sample the INT pin for a low-level signal?

Once each machine cycle Signup and view all the answers

What type of activation does NOT apply to the external hardware interrupts in the 8051?

Pulse triggered Signup and view all the answers

Where are the interrupt vector table locations set aside for INTO and INT1?

0003H and 0013H Signup and view all the answers

What is the formula used to calculate the physical address in memory?

Physical address = segment address + offset address Signup and view all the answers

Which register is used to enable and disable the external hardware interrupts?

IE register Signup and view all the answers

Which pointer register is responsible for storing the memory location of the next instruction to be executed?

IP - Instruction pointer Signup and view all the answers

What is the main role of the SI register in the context of memory addressing?

To store the offset of source data in the data segment Signup and view all the answers

Which flag in the flag register indicates that the result of a computation is zero?

ZF - Zero Flag Signup and view all the answers

What is the purpose of the carry flag (CF) in the 8086 flag register?

It indicates a carry out of MSB or a borrow in subtraction. Signup and view all the answers

Which part of the flag register contains control flags such as direction flag (DF) and interrupt flag (IF)?

Higher byte of the flag register Signup and view all the answers

Which of the following statements is true about the segment registers?

They store 16-bit segment base addresses. Signup and view all the answers

The parity flag (PF) is set to 1 when:

The lower byte of the result contains an even number of 1’s. Signup and view all the answers

What happens to the Stack Pointer (SP) when an instruction like POP AX is executed?

SP is incremented by 2 Signup and view all the answers

When the instruction PUSH BX is executed, which operation occurs first?

SP is decremented by 2 Signup and view all the answers

In string instructions, what operation occurs when DF = 0 after executing STOSB?

DI is incremented by 1 Signup and view all the answers

In the context of REP prefix with string instructions, what does REPNE/REPNZ do?

Repeats as long as CX is greater than zero and the result is non-zero Signup and view all the answers

Which of the following best describes the purpose of the LOOP instruction?

To execute a series of instructions a specified number of times Signup and view all the answers

What is the function of the REPE/REPZ prefix in string instructions?

Repeats until CX reaches zero and produced a zero result Signup and view all the answers

When executing a conditional transfer, which of the following instructions might be involved?

JE (Jump if Equal) Signup and view all the answers

What is the initial action of the REP prefix before executing a string instruction?

Decrements CX by 1 Signup and view all the answers

What is the purpose of the PSW (Program Status Word) in the 8051 microcontroller?

It monitors the program's status and holds information about the current execution. Signup and view all the answers

Which of the following correctly describes the function of the TXD pin in the 8051 microcontroller?

It is used to transmit data to be sent. Signup and view all the answers

How many sources of interrupts does the 8051 microcontroller provide?

5 sources Signup and view all the answers

Which registers are involved in managing serial data communication in the 8051 microcontroller?

SBUF, SCON, and PCON Signup and view all the answers

What is the role of ALE (Address Latch Enable) in the 8051 microcontroller?

It latches the address signals on Port P0. Signup and view all the answers

What does the PCON (Power Control) register manage in the 8051 microcontroller?

It controls the baud rate for serial communication. Signup and view all the answers

What range of addressable bits does the internal RAM of the 8051 microcontroller have?

128 bits Signup and view all the answers

Which mode is NOT included in the four programmable modes of serial data communication in the 8051?

Serial Data mode 4 (advanced multiprocessor mode) Signup and view all the answers

What instruction is used to push the accumulator onto the stack?

PUSH 0E0H Signup and view all the answers

Which register is associated with 8-bit addresses in register indirect addressing mode?

R0 and R1 Signup and view all the answers

What does the instruction 'POP 03' do?

Pops into register R3 Signup and view all the answers

In what addressing mode can the source memory only be accessed from program memory?

Indexed addressing mode Signup and view all the answers

What is a characteristic of the MOV instruction with the @ symbol?

It represents register indirect addressing mode. Signup and view all the answers

What will the instruction 'MOV @DPTR, A' accomplish?

It overwrites the content at the address pointed by DPTR with the value in register A. Signup and view all the answers

Which instruction format is correct for pushing register R1 onto the stack?

PUSH 01 Signup and view all the answers

If the content of R1 is 30H, what does the instruction 'MOV @R1, 80H' indicate?

Store 80H at internal RAM location 30H. Signup and view all the answers

Study Notes

Stack Pointer (SP)

The Stack Pointer (SP) is a register used to point to the top of a stack.
The stack is a data structure used to hold temporary data.
During a POP operation, SP is incremented by 2 (SP=SP+2).
During a PUSH operation, SP is decremented by 2 (SP=SP-2).

Instruction: PUSH

The PUSH instruction copies data from a source location to the stack.
The source can be a general-purpose register, a flag register, a segment register, or a memory location.
The addressing mode for PUSH is register indirect.

IN and OUT instructions are used for input and output operations respectively.
They are used to interact with peripherals connected to the processor.

Conditional Transfer

Conditional Transfer instructions allow for the transfer of program control based on the values of a condition code flag.

Arithmetic Instructions

Arithmetic instructions perform mathematical operations like addition, subtraction, multiplication, and division.

String instructions are designed for efficient manipulation of string data.
String instructions can copy, compare, and scan strings of bytes or words.
The direction flag (DF) determines the direction of string operations – forward or backward.

REP Prefix

The REP prefix is used to repeat string operations multiple times.
It uses the CX register as a counter.
REP instruction repeats an operation while CX != 0.
REPNE/REPNZ repeats an operation while CX != 0 and the previous operation resulted in a non-zero result.
REPE/REPZ repeats an operation while CX != 0 and the previous operation resulted in a zero result.

LOOP Instruction

The LOOP instruction repeats a block of code a specified number of times.
The number of repetitions is stored in the CX register.
LOOP decrements CX by 1 and jumps to a specified label if CX != 0.

Physical Address Calculation

The Physical Address is calculated by adding the Segment Address and the Offset Address: Physical Address = Segment Address + Offset Address

Registers:

IP (Instruction Pointer)
- Stores the memory address of the next instruction to be executed.
BP (Base Pointer)
- Used to access data in the stack segment.
SP (Stack Pointer)
- Used to access data in the stack segment.
SI (Source Index)
- Used to store the offset of source data in the data segment.
DI (Destination Index)
- Used to store the offset of destination data in the data or extra segment.

Flag Register

The Flag Register monitors the status of the processor and stores results of ALU operations.
It is divided into two parts: Condition Code Flags and Machine Control Flags
Condition Code Flags:
- SF (Sign Flag): Set when the result is negative.
- ZF (Zero Flag): Set when the result is zero.
- PF (Parity Flag): Set when the result has even number of 1s.
- CF (Carry Flag): Set when there is a carry out or a borrow.
Machine Control Flags:
- DF (Direction Flag): Controls the direction of string operations.
- IF (Interrupt Flag): Enables or disables interrupts.
- TF (Trap Flag): Activates single-step mode for debugging.

Interrupt Priority (IP) Register

The IP Register assigns priorities to various interrupt sources.
A bit value of 1 indicates high priority, and 0 indicates low priority.

Programming Timer Interrupts

Timers in the processor are programmable and can be configured for different functions.
When a timer expires, a timer interrupt signal is raised.

Programming External Hardware Interrupts

The 8051 has two external hardware interrupts: INT0 and INT1.
They can be triggered by a low-level signal (level-triggered mode) or by a change in the signal level (edge-triggered mode).
The IE register controls enabling or disabling interrupts.

Internal RAM and ROM

The 8051 has 128 bytes of internal RAM (00h to FFh), used for data storage and temporary variables.
The 8051 also has internal ROM, used for program storage.

Interrupt Control

Interrupts are events that can interrupt the normal flow of program execution.
They allow the processor to handle events like timer expires, serial port data received, and external pin changes.
The 8051 supports 5 sources of interrupts:
- 2 external hardware interrupts (INT0 and INT1)
- 3 internal interrupts (Serial Port, Timer 0, Timer 1)

Serial Data Communication

The 8051 serial port uses the SBUF(Serial Port Data Buffer), SCON (Serial Control), and PCON (Power Control) registers for communication.
Serial data communication involves sending and receiving bits one at a time.
Data is transmitted via the TXD pin and received through the RXD pin.
The 8051 supports four serial data communication modes: Mode 0, Mode 1, Mode 2, and Mode 3.

PSW (Program Status Word)

The PSW register holds the status of the current program.
It stores information about the program's state, including the carry flag, parity flag, auxiliary carry flag, and zero flag.

Stack Operations

The stack is a data structure used for temporary data storage.
PUSH and POP instructions are used to add data to and retrieve data from the stack.

Register Indirect Addressing Mode

In this mode, the address of the data is stored in a register.
The 8051 uses R0 and R1 registers for 8-bit addressing and DPTR for 16-bit addressing.

Indexed Addressing Mode

In indexed addressing mode, the address of the data is calculated by adding the content of a register (like A, PC or DPTR) to a constant offset.
The destination operand in indexed addressing mode is always register A.

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Description

This quiz covers the concepts of Stack Pointer (SP) and related instructions such as PUSH, IN, and OUT. Learn how data is manipulated in a stack and the role of conditional transfers and arithmetic instructions in computer programming. Test your understanding of these fundamental computer architecture concepts.