Lecture 9: Machine Language and Addressing

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Lecture 9 Machine Language and Addressing

• Lecturer
• Mr Robert Ross

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Overview

• Machine Language
• Addressing Modes
• Physical Address Calculation

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Machine Language

• Processors only understand machine language (also
  called object code or machine code)
• Machine language is a collection of bits used to
  specify different instructions
• Machine language is architecture specific

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Language Flow

• High level languages are complied to assembly
  language
• Assembly language is assembled into machine code
• Assembly language is a human readable
  representation of machine code

High Level Language (eg. C, Java)
Assembly Language
Machine Code
Compiled
Assembled
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Reading Machine Code

• Machine code can be decoded back into assembly
  language
• Machine code instructions are made up of several
  parts including
• Op-code bits to encode the instruction
• src The source operand defined by As and S-reg
• dst The destination operand defined by Ad and
  D-reg
• As The addressing bits responsible for the
  addressing mode used for the source (src)
• S-reg The working register used for the source
  (src)
• Ad The addressing bits responsible for the
  addressing mode used for the destination (dst)
• D-reg The working register used for the
  destination (dst)
• B/W Byte or word operation 0word, 1byte

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Reading Machine Code

• For the MSP430 there are 3 types of machine code
  formats
• Double Operand
• Single Operand
• Jump

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Double-Operand

• Two different memory locations are accessed
• Example instructions
• MOV
• ADD
• SUB

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Single-Operand

• Have an implicit source or destination (so that
  an additional one need not be specified)
• Example instructions
• RRA (Rotate Right)
• PUSH
• RETI

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Jump

• Jump commands have a separate format
• 10-bit offset allows a jump range /- 512 of the
  PC
• Examples
• JNE
• JMP
• JGE

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Examples

• Moving Register to Register
• Assembly mov R5, R6 (1 Cycle)
• Machine 0x4506 (0100010100000110)
• Moving Register to Memory
• mov R5, 0x0200 (4 Cycles)
• 0x4580 0x0200 (0100010110000000 0000001000000000)
• Adding 5 to the value in the Register
• add 5, R5 (2 cycles)
• 0x5035 0x0005 (0101000000110101 0000000000000101)
• http//mspgcc.sourceforge.net/assemble.html

OP-CODE
(R5)
(R6)
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Addressing Modes

• The MSP430 has 7 Addressing modes

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Addressing Modes - Analogy

• If someone asks you how to get to this room what
  answers could you give?
• GPS Coordinates (Absolute address)
• Goto Building X, turn right and walk 10 meters
  (Indirect address)
• From where you are now turn left and walk 50
  meters (relative address symbolic in TI
  assembly)
• Pick them up and take them here directly
  (Immediate address)
• Multiple ways to get someone to this room
• Multiple ways for the CPU to address areas within
  memory

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Register Addressing

• Operations directly between the contents in
  registers
• Examples
• MOV R5, R6
• ADD R7, R9

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Indexed Addressing

• The value in the register is added to the offset
  to calculate the address

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Symbolic Addressing

• Indirect form of addressing
• Format MOV 500, R5
• Rather than storing 500, X is stored, where 500
  PC X
• Address referenced as PC (at point X) X

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Absolute Addressing

• The actual physical address is stored
• Normally used for hardware peripherals

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Indirect Addressing

• Store addresses in registers
• Refers to the contents of the address which is
  stored in the register

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Indirect Autoincrement Addressing

• Same as indirect, except that the address in the
  source register is incremented (1 for byte
  operation, 2 for word operation)

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Immediate Addressing

• Source is a constant value
• Examples
• MOV 4Fh, R5 Moves the value 4F into R5
• ADD 21, R6 Adds the value 21 to R6

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Addressing Modes - Syntax

• Syntax for addressing modes
• Register R1
• Indexed 2(R5)
• Symbolic 500
• Absolute 0x5000
• Indirect _at_R5
• Indirect Autoincrement _at_R5
• Immediate 45 (use to signify immediate)
• 45 45 Decimal
• 45h 45 Hex
• 01001001b 01001001 Binary

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Physical Address Calculations

• The physical address is the real address where
  something is stored
• Because different addressing modes and offsets
  are used, the physical address needs to be
  calculated with care

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Physical Address Calculations

• What are the source and destination addresses?
• MOV 10(R5), 2(R6)
• Source 110
• Destination 202
• MOV 500, 5000
• Source 500
• Dest 5000
• MOV _at_R7, 504
• Source 500
• Dest 504

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Summary

• Computers understand machine language
• Assembly language is a human readable version of
  machine language
• Microprocessors have several different addressing
  modes, providing several methods to address memory