Instruction Set and Programming of 8085 Microprocessor

Jul 9, 2024

Lecture Notes: Instruction Set and Programming of 8085 Microprocessor

Chapter Introduction

  • Chapter: 12th Computer Science Board - Chapter 2
  • Focus: Instruction Set and Programming of 8085 Microprocessor

Motivation and Marks Breakdown

  • Total Paper Marks: 90 marks (with options write for 50 marks)
  • Chapter Contribution: 43 marks (almost half of the total marks)
  • Question Type Breakdown:
    • 1 mark question - 1 question: 1 mark
    • 3 marks questions - 4 questions: 12 marks
    • 5 marks questions - 6 questions (with option, 30 marks without option, approx. 10 marks scored)
    • Total tangible marks from chapter: 23 marks

Basics Refresher: Number Systems

  • Number Systems: Decimal, Binary, Octal, Hexadecimal
  • Focus: Hexadecimal Numbers
    • Decimal: Based on 10 numbers (0-9)
    • Binary: Based on 2 numbers (0 and 1)
    • Octal: Not frequently used
    • Hexadecimal: Based on 16 numbers (0-9, A-F)
  • Hexadecimal Representation:
    • Example: Decimal 10 = Hexadecimal A, 11 = B, ..., 15 = F
    • Practice: Convert Binary to Hex & vice-versa
  • Hexadecimal to Binary Conversion Example:
    • Hexadecimal F = Binary 1111, etc. (4 bits to represent)
  • Hexadecimal Representation in Programs:
    • Example: Memory contents and representation using тАЬHтАЭ

Important Symbols and Abbreviations

  • ADDR (Address): Always 16 bits. Represents memory location.
  • DATA: Generally 8 bits, but can be 16 bits in rare cases.
  • REGISTERS: (R1, R2, etc.) General-purpose registers (A, B, C, D, E, H, L)
  • FLAGS: Special status indicators (e.g., Carry Flag, Zero Flag, etc.)
  • MEMORY: Addressed by HL pair (MEM[HL] = value stored)
  • OPERATORS: (AND, OR, XOR): Logical operation indicators
  • MOV Instruction Example: MOV A, B means copy contents of B to A

Addressing Modes of 8085 Microprocessor

  • Register Addressing Mode: Operands are registers; MOV A, B
  • Direct Addressing Mode: Operands are memory locations; LDA 2000H
  • Register Indirect Addressing Mode: Addressed by register pairs (e.g., M = HL)
  • Immediate Addressing Mode: Operand is immediate data; MVI A, 55H
  • Implied Addressing Mode: No explicit operands; CMA (complement accumulator)

Instruction Size

  • Size Determination Example: MOV A, B (1 byte), MVI A, 23H (2 bytes)
  • Instruction Breakdown: LDA 2000H involves 3 bytes; Opcode (1 byte) + Address (2 bytes)

Instruction Set

Data Transfer Group

  • MOV dest, src: Transfer data between registers (MOV A, B).
  • MVI reg, data: Immediate data transfer (MVI A, 23H).
  • LDA addr: Load accumulator from memory (LDA 2000H).
  • STA addr: Store accumulator in memory.
  • LHLD addr: Load HL pair from memory (LHLD 2000H).
  • SHLD addr: Store HL pair to memory.
  • LDAX rp: Load accumulator pair data (LDAX B).
  • STAX rp: Store accumulator pair data.
  • XCHG: Exchange HL and DE contents.

Arithmetic Group

  • ADD R: Add register to accumulator; flags affected (ADD B).
  • ADI data: Add immediate data to accumulator (ADI 05H).
  • ADC R: Add register with carry.
  • SBB R: Subtract register from accumulator with borrow.
  • INR R: Increment register by one (INR B).
  • DCR R: Decrement register by one (DCR B).

Logical Group

  • ANA R: Logical and with register (ANA B).
  • XRA R: Exclusive OR with register (XRA B).
  • CMP R: Compare register with accumulator (CMP B).
  • RLC: Rotate accumulator left.
  • RRC: Rotate accumulator right.
  • CMA: Complement accumulator.
  • CMC: Complement carry.

Branching Group

  • JMP addr: Unconditional jump (JMP 2000H).
  • JC addr: Jump if carry (JC 2000H).
  • JZ addr: Jump if zero (JZ 2000H).
  • CALL addr: Call subroutine (CALL 2000H).
  • RET: Return from subroutine (RET).
  • RST n: Restart from specific address (RST 7).

Machine Control Group

  • NOP: No operation.
  • HLT: Halt the microprocessor.
  • DI: Disable interrupts.
  • EI: Enable interrupts.
  • RIM: Read interrupt mask.
  • SIM: Set interrupt mask.
  • SPHL: Copy HL to stack pointer.

Example Programs and Applications

  • Example application and detailed walk-through to follow in practical session or next lecture.

Conclusion

  • Emphasis on practicing instructions and understanding opcode conversions.
  • Next Steps: Preparing for programming exercises.

For more detailed notes and explanation of specific instructions, refer to further study materials or reach out on discussed communication platforms.

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