8086 Microprocessor and Addressing Modes

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Questions and Answers

What is the purpose of the CMP instruction?

  • To compare two values and set the flags accordingly. (correct)
  • To move data from memory to a register.
  • To add two values together.
  • To perform a subtraction operation and store the result in a register.

Which of the following flags is NOT affected by the CMP instruction?

  • Zero Flag (ZF)
  • Carry Flag (CF)
  • Parity Flag (PF) (correct)
  • Sign Flag (SF)

What is the value of the Carry Flag (CF) if the CMP instruction compares two values where the first operand is greater than the second operand?

  • undefined
  • 1
  • 0 (correct)
  • -1

What is the significance of the Zero Flag (ZF) being set after a CMP instruction?

<p>The two operands are equal. (D)</p> Signup and view all the answers

What are the possible values of the Sign Flag (SF) after a CMP instruction?

<p>0 or 1 (D)</p> Signup and view all the answers

What is the effect of the SCASB instruction on the flags if the value in AL is less than the value in the memory location pointed to by DI?

<p>CF = 1, ZF = 0, SF = 1 (A)</p> Signup and view all the answers

What is the effect of the SCASW instruction on the DI register if the Direction Flag (DF) is 0?

<p>DI is incremented by 2 (A)</p> Signup and view all the answers

How does the LODSB instruction work?

<p>It loads a byte from the memory location pointed to by SI into the accumulator (AL), and then increments SI by 1 (D)</p> Signup and view all the answers

Which of the following instructions is used to store a string of bytes into memory?

<p>STOS (C)</p> Signup and view all the answers

What is the purpose of the STOSB instruction?

<p>Store a byte from the AL register to a string (D)</p> Signup and view all the answers

Which of these instructions are used to manipulate strings? (Select all that apply)

<p>CMPS (A), STOSB (B), LODS (C), MOVS (G)</p> Signup and view all the answers

What value does the DI register hold after the STOSB instruction executes if the direction flag (DF) is set to 0?

<p>DI + 1 (D)</p> Signup and view all the answers

What happens if DF is set to 1 when STOSW is executed?

<p>DI - 2 (C)</p> Signup and view all the answers

Which instruction is used to halt the processor after setting an interrupt?

<p>HLT (C)</p> Signup and view all the answers

Which instruction is used to call a subroutine?

<p>CALL (D)</p> Signup and view all the answers

What signal is used to synchronize an external activity to the processor's internal operation?

<p>TEST (C)</p> Signup and view all the answers

Which signal is actively high and causes the processor to immediately terminate its current activity?

<p>RESET (C)</p> Signup and view all the answers

What is the purpose of the READY signal?

<p>To indicate the completion of a data transfer by a slow device or memory. (A)</p> Signup and view all the answers

What is the role of the 8284A clock generator in the READY signal?

<p>To synchronize the READY signal before it is sent to the 8086. (C)</p> Signup and view all the answers

Which signal is triggered during the last clock cycles of each instruction?

<p>INTR (D)</p> Signup and view all the answers

Which signal provides the basic timing for processor operation and bus control activity?

<p>CLK (B)</p> Signup and view all the answers

What is the significance of the 33% duty cycle in the CLK signal?

<p>It provides more time for the processor to process instructions. (C)</p> Signup and view all the answers

What is the size of the 8086's memory address space?

<p>1 MB (C)</p> Signup and view all the answers

Which register is used to hold the offset address of the top of the stack memory?

<p>SP (C)</p> Signup and view all the answers

Which of the following is NOT a segment register?

<p>IP (D)</p> Signup and view all the answers

How many bits are in the 8086's instruction pointer (IP)?

<p>16 (C)</p> Signup and view all the answers

What is the purpose of the BIU (Bus Interface Unit) in the 8086 architecture?

<p>To manage memory access (B)</p> Signup and view all the answers

Which register is used to hold the count value in SHIFT, ROTATE, and LOOP instructions?

<p>CX (B)</p> Signup and view all the answers

How many segment registers are there in the 8086 architecture?

<p>4 (D)</p> Signup and view all the answers

Which register is used to hold the index value of the destination operand for string instructions?

<p>DI (A)</p> Signup and view all the answers

What is the size of each segment in the 8086's memory addressing scheme?

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

What is the purpose of the Flag register in the 8086?

<p>To store the status of the CPU after an instruction is executed (C)</p> Signup and view all the answers

Which generation of Intel processors introduced the HCMOS technology?

<p>Fourth Generation (A)</p> Signup and view all the answers

What was the primary technology advancement introduced in the Second Generation Intel processors?

<p>NMOS technology (C)</p> Signup and view all the answers

What is the maximum physical memory space supported by the Third Generation Intel processors?

<p>16 MB (B)</p> Signup and view all the answers

Which of these Intel processors is a 16-bit processor?

<p>Intel 8086 (A)</p> Signup and view all the answers

What is the primary benefit of multiplexing signals in the early Intel processors?

<p>Overcoming pin limitations (C)</p> Signup and view all the answers

What is the total addressable memory space of the 8086 processor?

<p>16 MB (D)</p> Signup and view all the answers

Which of these features was introduced in the Third Generation Intel processors?

<p>Floating Point Hardware (C)</p> Signup and view all the answers

What is the primary difference between the Intel 8085 and the Intel 8086 processors?

<p>The 8085 is an 8-bit processor while the 8086 is a 16-bit processor (D)</p> Signup and view all the answers

Flashcards

CMP Instruction

Compares two values and modifies the flags accordingly.

Flags Set by CMP

CF, ZF, and SF indicate the comparison result: CF=Carry, ZF=Zero, SF=Sign.

If reg2 > reg1

CF=0, ZF=0, SF=0 if the second register is greater than the first.

If reg2 < reg1

CF=1, ZF=0, SF=1 if the first register is greater than the second.

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If reg2 = reg1

CF=0, ZF=1, SF=0 if both registers are equal.

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SCAS

Scan and compare string byte or word with accumulator.

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SCASB

Compare byte in AL with memory address MA; set flags accordingly.

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SCASW

Compare word in AX with memory address MA; adjust flags based on comparison.

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LODS

Load a string byte into AL or word into AX from memory address.

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DF Flag

Direction Flag indicating how SI or DI is incremented or decremented.

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TEST Input

A signal that enters a wait state when low, controlled by the WAIT instruction.

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WAIT Instruction

An instruction that causes the 8086 processor to pause execution until TEST is activated by hardware.

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READY Signal

Acknowledges from slow devices that they have completed data transfer to the processor.

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RESET Input

A signal that immediately terminates the processor's current activity when active HIGH for four clock cycles.

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CLK Signal

The clock input that provides basic timing for processor and bus control, usually an asymmetric square wave.

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INTR (Interrupt Request)

A triggered input that signals interrupts to the processor during the last clock cycles of instructions.

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8284A Clock Generator

Synchronizes signals from devices to provide a ready input to the 8086 microprocessor.

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Active Low Signal

A type of signal in which the active state occurs when the signal is low, important for TEST.

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Bus Interface Unit (BIU)

The component of the 8086 that handles memory addressing and I/O operations.

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Segment Registers

Registers that hold addresses of memory segments in 8086 architecture.

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General Purpose Registers

Registers like AX, BX, CX, and DX used for various arithmetic and logic operations.

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Accumulator (AX and AL)

Registers for storing results from arithmetic and logic operations; AX is 16-bit, AL is 8-bit.

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Base Register (BX)

Stores base values used in memory addressing by holding the base address.

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Stack Pointer (SP)

Points to the top of the stack in memory, crucial for function calls and local variables.

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Index Registers (SI and DI)

Registers that hold index values for source and destination data in string operations.

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Instruction Pointer (IP)

Register that contains the address of the next instruction to be executed.

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Total Memory Addressing

8086 can address 1 megabyte of memory divided into segments up to 64K each.

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Flag Register

Special register that indicates the status of operations; includes flags like CF and ZF.

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8086 Microprocessor

First 16-bit processor released by Intel in 1978.

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Addressable Memory Space

Organized into two banks of 512 kb each.

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First Generation Microprocessors

Used PMOS technology, incompatible with TTL, 4/8/16 bit processors.

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Second Generation Microprocessors

Utilized NMOS technology for higher speed and density.

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Third Generation Microprocessors

Introduced 32-bit processors, with significant memory capabilities.

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Fourth Generation Microprocessors

Low power version of HMOS technology, developed in the 1980s.

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Floating Point Hardware

Enables easier calculations involving fractions and decimals.

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Flexible I/O Port Addressing

Allows increased versatility in input/output management.

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STC

Sets Carry Flag (CF) to 1.

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CLC

Clears Carry Flag (CF) to 0.

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CALL

Calls a subroutine to execute code at another location.

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RET

Returns from a subroutine back to the calling location.

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JMP

Unconditional jump to a specified address or instruction without affecting flags.

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Study Notes

8086 Microprocessor

  • A 16-bit microprocessor developed by Intel.
  • First released in 1978.
  • Consistently evolved over decades, progressing from 4004 to Pentium 4.
  • Different generations of Intel microprocessors used different technologies, like PMOS, NMOS, HMOS, HCMOS, which affected the processor's features and capabilities (speed, transistors/ density, memory addressing).
  • Feature improvements included faster speed, packing density, more powerful interrupts, and higher memory addressing capability.
  • Package sizes evolved, indicating continuous shrinkage in chip dimensions and increased transistor count.

Addressing Modes

  • Used in instruction sets to describe the various ways to specify source operand addresses.
  • A program is a set of instructions intended to solve a problem.
  • Instructions are different directions a microprocessor can follow to execute a task.
  • Addressing modes allow the microprocessor to access data from various locations (registers, memory, ports).
  • Different methods for specifying where data comes from are:
    • Register addressing
    • Immediate addressing
    • Direct addressing
    • Register indirect addressing
    • Based addressing
    • Indexed addressing
    • Based indexed addressing
    • String addressing
    • I/O port addressing
    • Relative addressing
    • Implied addressing

Instruction Set

  • Data transfer instructions (MOV, XCHG, PUSH, POP, IN, OUT) move data between registers, memory, and ports.
  • Arithmetic instructions (ADD, ADC, SUB, SBB, INC, DEC, MUL, DIV, CMP) perform mathematical operations and comparisons.
  • Logical instructions (AND, OR, XOR, TEST, SHR, SHL, RCR, RCL) perform bitwise operations.
  • String manipulation instructions (MOVS, CMPS, SCAS, LODS, STOS) perform operations on strings of data.
  • Processor control instructions (STC, CLC, CMC, STD, CLD, STI, CLI, NOP, HLT, WAIT, ESC, LOCK) control the microprocessor's operation and interact with other systems.
  • Control transfer instructions (CALL, RET, JMP) transfer control flow within a program.
  • Conditional branch instructions provide conditional transfers of control flow.

Assemble Directives

  • Instructions to the assembler regarding the program being executed.
  • Control the generation of machine codes and the organization of the program.
  • Define program components (segments, procedures, macros).
  • Assign values to variables and allocate memory space.
  • Important assembler directives include DB, DW, SEGMENT, ENDS, ASSUME,ORG, END, PROC, ENDP, and various other directives as needed for particular tasks.

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