8086 Assembly Language Quiz
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Questions and Answers

What is the purpose of the MOV instruction?

  • To manipulate individual bits within a register.
  • To transfer data between registers, memory, and the processor. (correct)
  • To perform arithmetic operations on data.
  • To control the flow of execution in a program.

    • Which of the following is NOT a valid use of the MOV instruction?

  • Moving data directly from one memory location to another. (correct)
  • Moving data from a register to a memory location.
  • Moving data from one register to another.
  • Moving data from a memory location to a register.

    • What happens to the stack pointer (SP) register when data is pushed onto the stack?

  • It remains unchanged.
  • It is decremented by 2. (correct)
  • It is incremented by 2.
  • It is incremented by 4.

    • Which of the following instructions is used to load data from the stack into a CPU register?

    <p>POP</p> Signup and view all the answers

    What are the BYTE PTR and WORD PTR directives used for?

    <p>To indicate the size of data being moved.</p> Signup and view all the answers

    What is the relationship between the stack pointer (SP) register and the stack segment register (SS)?

    <p>The SS register contains the starting address of the stack, while the SP register points to the current top of the stack.</p> Signup and view all the answers

    Which of the following is TRUE about the PUSH and POP instructions?

    <p>They do not affect the flag register.</p> Signup and view all the answers

    Which of the following is an example of a valid 8086 instruction using the register addressing mode?

    <p>MOV BX, DX</p> Signup and view all the answers

    What is the main characteristic of the immediate addressing mode in the context of the 8086 processor?

    <p>The operand is always a constant value.</p> Signup and view all the answers

    Which of these statements is TRUE regarding the 8086 instruction set?

    <p>It permits memory-to-memory operations only for string instructions.</p> Signup and view all the answers

    What is the purpose of addressing modes in the 8086?

    <p>To define the types of operands and how they are accessed.</p> Signup and view all the answers

    Why is the instruction "MOV CL, AX" considered illegal in the 8086?

    <p>The destination register, CL, is too small to hold the contents of AX.</p> Signup and view all the answers

    Which of the following instructions is an example of using the immediate addressing mode with a decimal constant?

    <p>MOV CX, 625</p> Signup and view all the answers

    Why is the instruction "MOV DS, 0123H" considered illegal for the 8086?

    <p>The immediate addressing mode cannot be used with segment registers.</p> Signup and view all the answers

    What is the primary purpose of the MOV instruction when explaining 8086 addressing modes?

    <p>To illustrate how data is accessed and copied between different memory locations.</p> Signup and view all the answers

    How does the IN instruction transfer data from an input port to the accumulator?

    <p>The processor writes the input port's address to the data bus and reads the data</p> Signup and view all the answers

    What is the difference between the direct and indirect forms of the IN instruction?

    <p>The indirect form uses a port address stored in <code>DX</code>, while the direct form uses a fixed port number</p> Signup and view all the answers

    What would be the appropriate instruction to copy a word from port 30F8H to the AX register?

    <p>MOV DX, 30F8H; IN AX, DX</p> Signup and view all the answers

    What is the effect of executing the instruction IN AL, 80H if the data at port 80H is 22H?

    <p>The value 22H is stored in the <code>AL</code> register</p> Signup and view all the answers

    If you need to write a word of data from the AX register to a 16-bit port with the address stored in DX, what instructions would you use?

    <p>OUT DX, AX</p> Signup and view all the answers

    Consider the following instruction sequence:

    MOV DX, 30F8H
    OUT DX, AL.

    What is the purpose of this sequence?

    <p>Write a byte from the <code>AL</code> register to port 30F8H</p> Signup and view all the answers

    What is the difference between a SHORT jump and a FAR jump in the 8086 architecture?

    <p>A SHORT jump uses a relative address within the same segment, while a FAR jump uses an absolute address spanning segments.</p> Signup and view all the answers

    How does the 8086 processor determine if a jump instruction is a NEAR or FAR jump?

    <p>By analyzing the target address specified in the instruction.</p> Signup and view all the answers

    Which statement accurately describes the relationship between the Flags register and conditional jump instructions?

    <p>The Flags register stores the result of the last arithmetic operation, which is used by conditional jump instructions to determine if a jump will be taken.</p> Signup and view all the answers

    Which of these conditional jump instructions is used to jump to a label if the Zero Flag (ZF) is set to 1?

    <p>JZ label</p> Signup and view all the answers

    What is the primary difference between using JG/JL/JGE/JLE instructions and JA/JB/JAE/JBE instructions for conditional jumps?

    <p>JG/JL/JGE/JLE are used for signed comparisons, while JA/JB/JAE/JBE are used for unsigned comparisons.</p> Signup and view all the answers

    In the context of conditional jump instructions, which of these statements accurately describes the function of the Carry Flag (CF) in the Flags register?

    <p>The CF indicates whether the result of a subtraction operation resulted in a borrow.</p> Signup and view all the answers

    Which of these statements accurately describes the role of the IP register in the context of jump instructions?

    <p>The IP register stores the address of the next instruction to be executed.</p> Signup and view all the answers

    How does the processor decide whether to execute the next instruction in the program or jump to a different location based on the result of a conditional jump?

    <p>It examines the values of the status flags in the Flags register, such as the Zero Flag (ZF), Sign Flag (SF), and Carry Flag (CF), to make the decision.</p> Signup and view all the answers

    What is the primary purpose of the LOOP instruction in assembly language?

    <p>To repeat a series of instructions a specified number of times</p> Signup and view all the answers

    What condition must be met for LOOPZ to continue looping?

    <p>The zero flag must be set and CX must not equal 0</p> Signup and view all the answers

    Which instruction is the opposite of LOOPZ and will only continue if the zero flag is cleared?

    <p>LOOPNE</p> Signup and view all the answers

    How does the CX register behave after each execution of the LOOP instruction?

    <p>It decrements by 1</p> Signup and view all the answers

    What distinguishes strings in the 8086 assembly language from single byte or word operations?

    <p>Strings can perform operations on a collection of bytes or words</p> Signup and view all the answers

    What happens when the zero flag is cleared during execution of a LOOPZ instruction?

    <p>The loop will terminate</p> Signup and view all the answers

    In the given assembly language program for adding two numbers, where is the result stored if the sum is negative?

    <p>Offset 1103H</p> Signup and view all the answers

    What is the maximum length of a string that can be handled in the 8086 assembly language?

    <p>64KB</p> Signup and view all the answers

    What is the purpose of the DS register in the indexed relative addressing mode?

    <p>It holds the base address of the data segment.</p> Signup and view all the answers

    Which of the following is a valid example of the indexed relative addressing mode?

    <p>MOV CX, [SI] + 5</p> Signup and view all the answers

    What is the maximum allowable value for the const value used in indexed relative addressing mode?

    <p>-128 to 127</p> Signup and view all the answers

    Which of the following is NOT a characteristic of the indexed relative addressing mode?

    <p>It can be used to access data in the stack segment.</p> Signup and view all the answers

    Which of the following assembly language instructions demonstrates the use of the indexed relative addressing mode in accessing data?

    <p>MOV BL, [SI] + 5</p> Signup and view all the answers

    The indexed relative addressing mode is similar to the based relative addressing mode except for the fact that:

    <p>The <code>DI</code> or <code>SI</code> register is used instead of <code>BX</code> or <code>BP</code> as the offset register.</p> Signup and view all the answers

    In the instruction MOV CL, [DI] + 20, what does 20 represent?

    <p>The displacement value added to the offset value.</p> Signup and view all the answers

    What is the most accurate way to describe the purpose of directives in assembly language programming?

    <p>Directives provide instructions to the assembler about how to translate the assembly code into machine code.</p> Signup and view all the answers

    Study Notes

    Microprocessor and Assembly Language Programming

    • The Intel 8086 processor has approximately 117 instructions and about 300 opcodes.
    • Instruction sets can include no operand, single operand, or two operand instructions.
    • 8086 instructions generally do not permit memory-to-memory operations, except for string instructions involving array operations.
    • The processor uses different methods to access memory, collectively called addressing modes.
    • The number of addressing modes is fixed during microprocessor design.

    8086 Addressing Modes

    • The 8086 processor uses seven distinct addressing modes.
    • These modes include Register addressing, Immediate addressing, Direct addressing, Register indirect addressing, Based relative addressing, Indexed relative addressing, and Based indexed relative addressing.
    • MOV instructions are utilized to illustrate addressing modes.

    8086 Addressing Modes (Continued)

    • Register Addressing Mode: Registers hold data to manipulate. Example: MOV BX, DX; copies DX to BX.
    • Immediate Addressing Mode: The source operand is a constant. Example: MOV AX, 2550H; moves 2550H into AX. Cannot be used with segment registers or the flag register.
    • Direct Addressing Mode: Data is stored in a memory location, and the address is immediately following the instruction. Example: MOV DL, [2400H]; moves the contents of DS:2400H into DL.

    8086 Addressing Modes (Continued)

    • Register Indirect Addressing Mode: The memory address is held in a register (e.g., SI, DI, or BX) combined with the DS register to form a 20-bit address. Example: MOV AL, [BX]; moves the contents of DS:BX into AL.

    8086 Addressing Modes (Continued A)

    • Based Relative Addressing Mode: Calculates the effective address using a base register (BX or BP) and an 8-bit displacement value. DS is used for BX, and SS for BP. Example: PA = DS * 10H + BX + const.

    8086 Addressing Modes (Continued B)

    • Indexed Relative Addressing Mode: Similar to based relative, but uses SI or DI registers instead of BX or BP. Example: PA = DS * 10H + DI + const.

    Summary of Addressing Modes

    • Table 3-1 summarizes offset registers for various segments (e.g., CS, DS, ES, SS). This table shows the registers that can be used in combination with specific segment registers for calculations of memory addresses.

    Introduction To Assembly Language Programming

    • Program execution involves fetching binary information from memory, decoding it to determine the instruction represented.
    • An assembler converts the source file to an object file containing the machine-executable binary code.
    • Assembly language programs are sequences of statements or lines, which can be assembly instructions or pseudo-instructions (directives).

    Directives and Sample Program

    • Labels in assembly language allow referencing code lines by name (max 31 characters).
    • The label ends with a colon if it refers to an opcode, and without if it is a directive.
    • Mnemonic and operand fields together accomplish the program's intended tasks.
    • Example directives: DB, PROC, END, and ENDP.

    Model Definition

    • The .MODEL directive selects the size of the memory model.
    • Example: .MODEL SMALL
    • A specific memory model controls how memory is organized

    Segment Definition

    • Every line in an assembly language program corresponds to an x86 CPU segment register (CS, DS, SS, ES).
    • The .STACK directive reserves memory for the stack.
    • The .DATA directive defines the data area.
    • The .CODE directive defines the code area.

    Stack Segment

    • The .STACK 64 directive reserves 64 bytes of memory for the stack.

    Data Segment

    • The .DATA directive defines areas used for data storage.
    • Example: DATA1 DB 52H, DATA2 DB 29H.

    Data Segment (DB Directive)

    • The DB directive allocates byte-sized chunks of memory.
    • It can define numbers in decimal, binary, or hexadecimal format, and ASCII strings.
    • Data defined in the .DATA segment can be accessed by the .CODE segment using their labels (e.g., DATA1, DATA2).

    Code Segment Definition

    • The first line after a .CODE directive is a PROC directive, defining procedures within the code.
    • A procedure is a set of instructions designed to perform a specific function; it is used to organize code.
    • A label for the PROC and ENDP directives must be the same.
    • The PROC directive may include FAR or NEAR options, while FAR procedures are designed for external calls.

    Code Segment Definition (cont)

    • Before executing a program, the operating system initializes segment registers for CS and SS.
    • Segment registers DS and ES are then initialized by the program. The code that does data initialization (as in moving data from memory to a register) typically is in the beginning of code section
    • The instructions MOV AX, @DATA and MOV DS, AX are used to load the address of the data segment into the DS register.

    Code Segment Definition (cont...)

    • The MOV AH, 4CH and INT 21H instructions return program control to the operating system.
    • Programs use the MASM assembler and LINK linker to generate executable files.
    • Steps: Edit program (creating an ASCII text file), Assemble, Link, run the executable.

    Introduction to Assembly Language Programming (part 2)

    • The .asm file is compiled to an object file and a list file.
    • The .lst file is helpful for debugging because it shows opcodes, errors, and more.
    • The .obj file must be converted into an executable (.exe) file.

    Data Types and Data Definitions

    • The 8088/86 processor supports various data types (8-bit, 16-bit).
    • The ORG directive indicates the starting address of a memory block.
    • Numbers are usually in hexadecimal unless explicitly marked as decimal (e.g., 2591 instead of 2591H if decimal).

    Data Types and Data Definitions (cont...)

    • The DB directive allocates memory in byte-sized chunks and can define numeric and ASCII data.
    • The DUP directive repeats a data pattern multiple times, e.g., 5 DUP(2 DUP(99)).

    Data Types and Data Definitions (cont...)

    • The EQU directive associates a symbolic name (constant) with a value, allowing simple modification of values used across multiple sections of code.

    DEBUG Program Instruction Set

    • DEBUG is a program for closely monitoring program execution.
    • DEBUG can be used for examining and altering memory contents, entering and running programs, and stopping programs at particular points.
    • DEBUG uses commands like A, D, E, G, R, T, U to manipulate and inspect memory, registers, and instructions.

    DEBUG Program Instruction Set (cont...)

    • DEBUG instructions. A example: A<starting address> (assembles), D <start address>[<end address>] or <number of bytes> (dumps), E <address> [<data list>] (enters data), G <start address> [<end address>] (executes code). Other instructions: T, and U;

    Examining the Stack in DEBUG

    • The stack grows "upward" in memory.
    • When data is pushed onto the stack, the stack pointer decreases.
    • When data is popped off the stack, the stack pointer increases.

    Quiz 2 Questions

    • DUP duplication in assembly language; advantages and disadvantages.
    • Difference between the trace command and go command in DEBUG.

    Instruction Set of 8086 (Instruction Groups)

    • Instructions are grouped into categories (data transfer, string, loops, arithmetic, bit manipulation, subroutine/interrupt, and processor control)

    Data Transfer Instructions (MOV)

    • MOV copies data between registers, registers and memory (but not memory to memory), byte or word-sized data.
    • MOV instruction doesnt alter any flags.

    Data Transfer Instructions (CONT)

    • Using BYTE PTR and WORD PTR helps specify the size (byte or word) of operands when needed
    • Using registers SP and SS is important to manage the stack.
    • The PUSH instruction stores the contents of a register (or memory) onto the stack. The SP decrements after each PUSH. The POP instruction moves data from the stack into a register (or memory location). The SP increments after each POP.

    Data Transfer Instructions (PUSH and POP).

    • PUSH and POP are used to load data into or receive data from the stack memory. Stack is referenced by SS and SP registers
    • PUSH instructions store a CPU register into the stack
    • POP instructions load the stack contents into a CPU register.
    • There's no PUSH AL instruction (must use 16-bit register)
    • No flags are affected when PUSH and POP are executed
    • Stack grows 'upward' in memory (toward higher addresses).

    Data Transfer Instructions (PUSH and POP; cont)

    • Examples of PUSH instructions. Example: PUSH BX, PUSH DS, PUSH TABLE[BX], PUSH AL

    Data Transfer Instructions (PUSHA)

    • PUSHA saves all 16-bit registers (AX, CX, DX, BX, SP, BP, SI, DI) onto the stack in a particular order.

    Data Transfer Instructions (POPA)

    • POPA retrieves the 16-bit registers (DI, SI, BP, SP, BX, DX, CX, AX) from the stack in the reverse order of a PUSHA

    Data Transfer Instructions (IN and OUT)

    • The IN instruction copies data from an input port to a CPU register (AL or AX).
    • The OUT instruction copies data from a CPU register (AL or AX) to an output port.
    • Port addresses can be either 8-bit or 16-bit. See specific examples of IN AL, and IN AX, etc for addresses; see examples of OUT instruction and its use

    Data Transfer Instructions(LEA)

    • LEA (Load Effective Address) loads the offset of a memory operand into a register.
    • This is different from simply moving data from a memory operand into a register. It only moves the address.

    Data Transfer Instructions (XCHG)

    • XCHG swaps the contents of two operands, one register, the other potentially a register or memory location

    Loops and Jumps Instructions (JMP)

    • JMP (jump) instructions change the path of program execution to a new location. JMP is unconditional: it executes without any condition needing to be met. There are multiple types, like SHORT, FAR, and NEAR JMP, each impacting the program address differently.

    Loops and Jumps Instructions (J cond)

    • Conditional jump instructions transfer control to a new location only if a specified condition is true. The specific condition is based upon processor flags.

    Loop Instructions (LOOP, LOOPE/LOOPZ, LOOPNE/LOOPNZ).

    • LOOP instructions repeat a sequence of instructions a specified number of times (controlled by the counter in the CX register)
    • LOOP instructions automatically decrement the CX register after each iteration
    • LOOPE/LOOPZ will jump only if the zero flag is set and the CX register is not zero.
    • LOOPNE/LOOPNZ will jump only if the zero flag is not set and the CX register is not zero.

    String Instructions

    • String instructions perform operations on series of operands (bytes or words) in consecutive memory locations..
    • It handles entire sequences of data rather than just individual items. Examples: CMPS,

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    Description

    Test your knowledge on the 8086 assembly language instructions, addressing modes, and stack operations. This quiz covers various aspects, including the MOV, PUSH, and POP instructions, as well as understanding the stack pointer and segment registers.

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