Chap#2 An Introduction to the Pentium Microprocessor
   Objective

• Real Mode and Protected Mode Operation
• Register Set of Pentium
• Addressing Capabilites and Data Type
• Addressing Mode and Instruction Type
• Interrupt
• Hardware, Software of 8088
• Difference of 8086 and 80286, 80386, 80486 and Pentium Microprocessor

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2.1   Introduction

• Pentium offers compatibility with 80x86 machine with new architectural improvement

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2.2   Real Mode and Protected Mode Operation

• Addressing Space (Ref Tab)
• 80286 ~ Pentium operated in

   1)  Real Mode (run in DOS, Like very first 8086)
   2)  Protected Mode (run in Window OS) support for
            * Multitasking
            * Virtual memory addressing
            * Memory management
            * Protection

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2.3   The Software Model of the Pentium (Fig 2.1)

• 4 Data Register : EAX, EBX, ECX, EDX
• 5 Pointer/Index Register

    * ESP : Stack Pointer
    * EBP : Base Pointer
    * ESI : Source Index
    * EDI : Destination Index
    * EIP : Instruction Pointer
• 6 Segment Register : to access memory and I/O
• 1 Flag Register : to indicate result of ALU Instruction

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2.4   A Functional Description of the Pentium

• Pentium Architecture (Fig 2.2)
• 2 pipeline U and V for Executing 80x86 Instruction
• A Floating Point Unit for Executing 80x87 Instruction
• U and V pipe can exe at same time
• 32 Bit Address Bus
• 64 Bit Data Bus
• Bus Unit perform burst read and writes of 32 Byte to memory
• Bus cycle pipeline , allows 2 bus cycle at same time
• 8KB Instruction Cache provide quick access
• Branch target buffer and Prefetch buffer work together
• Prefetch buffer copy 32 Byte code in 1 clock
• Use branch prediction to maintain a steady flow of instruction into the pipelines
• 8KB Data Cache (separate)
• Both Code and Data cache may be enable/disable with H/W or S/W
• TLB (Translation Lakeside Buffer) which converts logical address into physical addresses when virtual memory is employed
• Used U and V pipe , one FP instruction may be execute at a time

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2.5   Pentium Processor Register

• Real Mode (virtual 8086) address bus 20 Bit
• Segment Register :

    * CS, DS, SS, ES, FS, GS are all 16 Bit  register
    * Real Mode Segment = 2^16 = 64 KB
    * Generating 20 bit address (Fig 2.3)
    * In Protected Mode
        The segment register are use as selector
        that point to predefined segment descriptors
• General Purpose Register :

    AX, BX, CX, DX, BP, SI and DI
    have some specific role
    * Accumulator(AX) is used in mul & div operation
        and I/O port
    * Count Register (CX) use as counter in loop operation
        CL use as counter in shift/rotate operation
    * Data Register (DX) is used in mul & div operation
        and I/O pointer
    * Source Index (SI) & Destination Index (DI)
        are used as pointer in string operation
    * Pentium operated in real mode
        it register size is 16 bit
        but can take 32 bit , by "operand size prefix 66H
    * Example 2.1 (by MASM)
        Distance : 93,000,000 miles (Sun to Earth)
        Light Speed : 186,000 miles/sec
        Determine Time : ?  (500 sec)
• Flag Register :

    * Lower word of flag register (Fig 2.4)
    * Control Flag :
            IF : Interrupt Flag
            DF : Direction Flag
            TF : Trap Flag
    * Status Flag :
            CF : Carry Flag
            PF : Parity Flag
            AF : Auxiliary Carry Flag
            ZF : Zero Flag
            SF : Sign Flag
            OF : Overflow Flag
            NT : Nested Task
            IOPL : I/O Privilege Level

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2.6   Pentium Data Organization

• Bits , Bytes , Words (Fig 2.5)
• Byte-Swapping (Fig 2.6)
• Assembler Directives (DB, DW, DUP, EQU )

    * DB : define byte
    * DW : define word
    * DUP : duplicate
    * EQU : equate

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2.7   Pentium Instruction Type

• 1. Data transfer instruction (MOV)
• 2. Arithmetic instruction (ADD)
• 3. Bit manipulation instruction (AND)
• 4. String instruction (CMPS)
• 5. Program transfer instruction (CALL)
• 6. Processor control instruction (CLC)

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2.8   Pentium Addressing Modes

• Real Mode Addressing Space (Fig 2.7)
• Addressing Mode

1)  Immediate : e.g.   MOV    CX,1024
2)  Register Addressing : e.g.   ADD    AL,BL
3)  Memory Addressing :
    *  Direct : e.g.  MOV    AX,[3000]
    *  Register Indirect : e.g.  MOV    BX,[SI]
    *  Based :  e.g.  MOV    AX,[BX+4]
    *  Indexed :  e.g.  MOV    [DI-8],BL
    *  Based Indexed : e.g.  MOV    [BP+SI],AH
    *  Based Indexed with Displacement :
                e.g.  MOV    CL,[BX+DI+2080]
    *  String Addressing :
                e.g.  MOVSB (use SI & DI as pointer)
    *  Port Addressing :
                e.g.  IN    AL,40
                    OUT    80,AL
• 32-Bit Addressing Mode 
      *  Generating a 32-bit address (Fig 2.8)
      *  66H : Operand size prefix byte
      *  67H : Address size prefix byte (Exa 2.2)

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2.9   Interrupts

• Hardware Interrupt
      *  NMI : nonmaskable Interrupt
      *  INTR : maskable Interrupt
• Software Interrupt
      *  INT 0 ~ INT 255
      *  INT 0 : divide error
      *  INTO = INT 4 : interrupt on overflow
• Interrupt Vector Table (Fig 5.1)
      *  for storage ISR table
      *  ISP : Interrupt Service Routine
• A brief look at DOS  INT  21H
      *  vector address = 21H * 4 = 84H
      *  ISR address ==> (-Dump) 0726:16B4
      *  e.g.   MOV    AH,2CH    ;get system time 
                  INT        21H          ;DOS call
          : ENTRY : AH <== 2CH
            EXIT     : CH = hrs
                            CL = min
                            DH = sec
                            DL = hundred of sec

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2.10   The 8086 : the first 80x86 machine

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2.11   A summary of the 80286

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2.12   A summary of the 80386 

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2.13   A summary of the 80486 

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2.14   A summary of the pentium

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2.15   Summary 

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