Jawaharlal Nehru Technological University Hyderabad B. Tech III Year MICROPROCESSORS AND MICROCONTROLLERS Previous Question Paper (August/September - 2021 - R18)

The 8086 microprocessor provides various addressing modes to specify the operand location for an instruction. These are categorized as follows:

• Immediate Addressing Mode: The operand is specified directly within the instruction. Example:

  MOV AX, 1234H

• Register Addressing Mode: The operand is located in one of the 8-bit or 16-bit general-purpose registers. Example:

  MOV AX, BX

• Direct Addressing Mode: The 16-bit effective address is provided directly in the instruction. Example:

  MOV AX, [1200H]

• Register Indirect Addressing Mode: The effective address is stored in a register (BX, BP, SI, or DI). Example:

  MOV AX, [BX]

• Based Addressing Mode: The effective address is the sum of a base register (BX or BP) and an 8-bit or 16-bit displacement. Example:

  MOV AX, [BX + 05H]

• Indexed Addressing Mode: The effective address is the sum of an index register (SI or DI) and a displacement. Example:

  MOV AX, [SI + 05H]

• Based-Indexed Addressing Mode: The effective address is the sum of a base register, an index register, and an optional displacement. Example:

  MOV AX, [BX + SI + 05H]

• Relative Addressing Mode: Used in branch instructions where the target address is calculated by adding an 8-bit signed displacement to the Instruction Pointer (IP). Example:

  JMP label

Arithmetic and logical shift instructions in 8086 are used to manipulate bits within a register or memory location.

• Arithmetic Shift Left (SAL/SHL): Shifts bits to the left, filling the LSB with 0. It is equivalent to multiplying by 2. Example:

  MOV AL, 05H; AL=00000101
  SAL AL, 1; AL=00001010 (0AH)

• Arithmetic Shift Right (SAR): Shifts bits to the right, preserving the MSB (sign bit). It is equivalent to signed division by 2. Example:

  MOV AL, 0F0H; AL=11110000
  SAR AL, 1; AL=11111000 (0F8H)

• Logical Shift Right (SHR): Shifts bits to the right, filling the MSB with 0. Used for unsigned division. Example:

  MOV AL, 0F0H; AL=11110000
  SHR AL, 1; AL=01111000 (78H)

These instructions are essential for efficient multiplication, division, and bit-masking operations in assembly programming.