Manav Goyal

8086 Microprocessor - Microprocessor And Interfacing

  • 8085 Architecture
    • 8-bit processor size, 16-bit address bus, Can access up to 64 Kb
    • Doesn't support Instruction queue, pipelined architecture and Multiprocessing
    • Can address 28=256 I/O
    • Low cost
    • Only supports integer and decimal
    • Memory space is not segmented
  • 8086 Architecture
    • Enhanced version of 8085 microprocessor designed by intel in 1976
    • Powerful instruction set
  • Operations Modes
    • Max Mode
      • It is a multiprocessor system
      • Can handover the task to other component
    • Min Mode
      • It is a single-processor system
  • Features
    • It is a 40 Pin IC, 16-bit processor
    • Its operating voltage is 5 Volt, Frequency is 5 Mega-Hertz
    • Total memory addressing capacity is 1 Mb (External)
    • 16-Bit data bus & 20-bit address bus
    • Can address 216=65,536 I/O
    • It has 14 16-Bit registers
    • Higher throughput
  • Microprocessor based system
    • Basic
      • These are electrical system
      • Image Not Loaded
    • Types
      • System Hardware
        • Discrete components -=> Microprocessor, Memory, I/O
        • Components connected by bus -=> Address, Data, Control
      • System Software
        • Group of programs that monitors the function of entire system
      • MPU communicate with Memory & I/O using System bus
        • Address bus
          • Unidirectional bus, Connected to memory and i/o
          • Processor wants to know the address of external device (Not other way as there is only 1 processor)
        • Data bus
          • Bidirectional bus
          • Transfers binary data and instructions
        • Control lines
          • It reads and writes timing signals
  • Internal 8086 Architecture
    • Image Not Loaded
    • Divided into 2 independent functional units
      • Bus interface unit
        • Functions
          • Fetch the instruction or data from memory
          • Write the data to memory
          • Write the data to ports
          • Reads data from ports
        • Functional Parts
          • Instruction pointer (IP)
            • It is a 16-bit register that keeps the address of memory location of coming instruction to be executed
          • Segment register
            • The memory space (1 Mb) is segmented into 4 blocks
            • Each block specified by register with maximum size 64 Kb
              • Code Segment (CS)
              • Data Segment (CS)
              • Stack Segment (CS)
              • Extra Segment (CS)
          • Instruction queue
            • BIU performs its operations in parallel with execution unit
            • BIU fetches instruction bytes while execution unit is executing operations
            • The prefetched instruction is saved in group of high speed registers known as instruction queue
      • Execution unit
        • Functions
          • To tell BIU where to fetch the instruction or data from
          • To decode instruction
          • To execute instruction
          • Contains the control circuitry to perform various internal operations
        • Functional Parts
          • General purpose register (GPRs)
            • 8086 processor consists of 4 GPR, Each of size 16-bit
              • AX, BX, CX, DX
            • Can use each of these as 2 8-bit registers
              • AH AL, BH BL, CH CL, DH DL
          • Pointer & Indexed register
            • Pointer
              • Stack pointer
              • Base pointer
            • Indexed
              • Source index
              • Destination index
          • ALU
            • 16-bit, Performs arithmetic and logical operation 8-bit and as well as 16-bit
          • Flag register
            • 16-bit
            • Image Not Loaded
            • 7 flags unused, Remaining 9 flags are divided into 2 categories
              • Status flag = 6
                • Carry, Auxiliary, Zero, Sign, PArity, Overflow
              • Control flag = 3
                • Direction, Interrupt enable, Trap
          • Timing & Control unit (CU)
            • CU directs all internal operations and also responsible for generation of control signal
  • Pin Diagram
    • 40 pin (DIP)
    • Image Not Loaded
  • Physical Address of 8086
    • Memory Segmentation
      • Total memory size is divided into segments (area in memory) of various sizes
    • Data is stored as bytes and each byte has some specific address
    • 8086 has 20 lines address bus
      • Memory can be addressed as 220 = 1 Mb
      • Address ranging from 00000H to FFFFFH
    • 8086 has 4 different types of segment -=> Each 16-bits, Each registers stores the base address (Starting address)
      • Code Segment
      • Data Segment
      • Stack Segment
      • Extra Segment
    • Convert 16-bit into 20-bit
      • BIU appends OH to LSB of address
      • Effective Address = Starting + Offset
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