Todays Topics

• Computer System Architecture
  • Registers, Memory, Peripherals
• Specifics on the 80x86
  • Registers, Memory, Peripherals
• Hints for MP0

Computer System Architecture

• Processor

  • A state machine
  • Opcodes
  • Perform operations (AND, OR, NOT, ADD, SUB)
  • Read and write data in memory

• Registers

  • Local processor storage: accumulator, pointers
  • Used for MOV operation

• Flags

  • Set by CMP, ADD (for overflow), etc.
  • Used by JE, JL, JLE, ... to condionally branch

• Memory

  • Data Types
    • Numbers
      • bit (eg: 1)
      • nibble = 4 bits
      • DB:byte = octet = 8 bits
      • DW:Word = 2 bytes = 16 bits (80x86 terminology)
      • DD:DoubleWord = 4 bytes = 32 bits (80x86 terminology)
      • Intel uses little endian format (i.e., LSB at lower address)
      • Signed Integers (2's complement)

    • Text
      • Letters and characters (7-bit ASCII standard)
        • 'A'=65=0x41
        • Extended ASCII (8-bit) allows for extra 128 graphics/symbols)
      • Collecition of charactors = Strings
      • Collection of Strings = Documents

    • programs
      • Commands (MOV, JMP, AND, OR, NOT)
      • Collections of commands = subroutines
      • Collection of subroutines = programs

    • Floating point numbers (covered later)
    • Images (GIF, TIF, JPG, BMP)
    • Video (MPEG, QuickTime, AVI)
    • Audio (voice, music)

  • Example

    Address	Data (8-bits)	Interpretation
    0xFFFFF
    ...
    0x75000	0x55	byte
    ...
    0x70008	'$'	string
    0x70007	'6'
    0x70006	'0'
    0x70005	'3'
    0x70004	' '
    0x70003	'S'
    0x70002	'C'
    ...
    0x60511	0x12	word	4x1 integer array of 16-bit words
    0x60510	0x34
    0x6050F	0x12	word
    0x6050E	0x34
    0x6050D	0x12	word
    0x6050C	0x34
    0x6050B	0x12	word
    0x6050A	0x34
    ...
    0x60013	0x12	dword
    0x60012	0x34
    0x60011	0x56
    0x60010	0x78
    ...
    0x55504	0xFE	JE -2	Program
    0x55003	opcode
    0x55002	0x02	ADD AL,2
    0x55001	opcode
    ...
    0x00000

    • Single byte stored at 0x75000
    • 32-bit integer stored at 0x60010 = 0x12345678
    • Program starts at 0x55001
    • 'CS306' string begins at 0x70002 (Terminated by '$')
    • 4x1 Vector of 16-bit words stored at 0x6050A-0x60511

  • Quiz

• Peripherals

  • Input/Output devices:
  • keyboard
  • disks
  • video adapter
  • sound cards

Specifics on the 80x86

• Registers

  • Note: 32-bit registers are not available on the 8086, 8088, or 80286
    
  
  • In the next lecture, we will cover typical usage of the registers.
  • A discussion about the use of registers in your programs

• Memory

  • Operates in Real Mode by default (20-bit addressing)
  • Addresses formed as a Segment:Offset
    
    The diagram above shows the generation of a linear address from a segment:offset address. The segment is a 16-bit field. The offset is also a 16-bit field. To perform the calculation, the segment is shifted left by 4 bits (1 nibble). The numbers are then added. The calculation is most easily done with hex addition.

  • Examples
    • Linear address for Segment:Offset=2222:3333 = 25553
    • Segment:offset address for Linear address=25553:
      • Many Answers - One possibility: 2222:3333
      • Many Answers - One possibility: 2000:5553

  • Segments provide a 2^16 (64 kByte) window into memory.

  • Use of segments
    • CS: Code segment - Your program
    • DS: Default segment - Your data and variables
    • SS: Stack segment - Temporary storage

    

• Peripherals

  • Memory-mapped devices
    • BIOS: 0xF0000-0xFFFFF (bootstrap, I/O calls)
    • Video: 0xA0000-0xBFFFF and vBIOS: 0xC0000-0xC7FFF

  • I/O mapped devices (Sound card, com ports, parallel port)
    • I/O addresses different than Memory addresses (due to I/O signal on ISA bus)
    • Address Range: 0x0000 - 0xFFFF (16-bit)

  • Interrupts
    • PIC: Programmable Interrupt Controller
    • Notifies the CPU when an event has occured
      • Timer [update clock]
      • Serial I/O [input data]
      • Parallel I/O [ready]
      • Network adapter [packet arrived]

• Processor

  • CISC: Complex Instruction Set Computer)
    The 80x86 supports over 20,000 instructions (and permutations). Systemically, we will cover most of these in the following three lectures. Some operations (such as ASCII-based addition) are not relevant to this course and will not be discussed.

Hints for MP0

• Basic Instructions

  Operation (example)	Function
  MOV AX, CSEG	Move contents of Code segment register to the AX register.
  MOV DX, constant	Load the register DX with a fixed value
  INC AX	Increment register AX
  CALL procedure	Call a procedure. A return address will go on the stack
  CMP AL, constant	Compare the register AL with a constant. Set Flags
  JE label	If flags indicate that previous compare was equal, jump to the address of the address defined by label. A GOTO statement.