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Physics 413 Chapter 2

Physics 413 Chapter 2. 6800 Architecture. A. B. X. SP. PC. CCR. Straight-line Programming. In Paris they simply stared when I spoke to them in French ; I never did succeed in making those idiots understand their own language Mark Twain , The Innocents Abroad , 1869.

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Physics 413 Chapter 2

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  1. Physics 413Chapter 2

  2. 6800 Architecture A B X SP PC CCR

  3. Straight-line Programming In Paris they simply stared when I spoke to them in French ; I never did succeed in making those idiots understand their own language Mark Twain , The Innocents Abroad, 1869

  4. My First Program • CLRA Clears accumulator A ( A = 0 ) • INC A This instruction does this: A + 1 A • WAI Stop (Wait)

  5. Op-codes Assembly LanguageMemory LocationOp-codes CLRA 0000 4F INCA 0001 4C WAI 0002 3E

  6. My Second Program LDAA # $ 12 ADDA # $ 15 WAI

  7. Object Code . . . Program # 2 Assembly LanguageMemory LocationOp-codes LDAA # $ 12 0000 86 0001 12 ADDA # $ 15 0002 8B 0003 15 WAI 0004 3E

  8. Addressing Modes • Inherent (implied) : Simplest with no operand. One-byte op-code. Examples: INCA and CLRA • Immediate : Operand specified is immediate (no memory access). Examples: LDAA # $ 12 and ADDA # $ 15

  9. Immediate and Direct Modes • Immediate LDAA # $ 12 Load 12 • op-code 86 12 • Direct LDAA $ 12 Load from memory 0012 • op-code 96 12

  10. My Third Program Assembly LanguageMemory LocationOp-codes LDAA # $ 04 STAA $ 15 LDAA # $ 08 ? ? ADDA $ 15 WAI

  11. My Third Program Assembly LanguageMemory LocationOp-codes LDAA # $ 04 0000 86 04 STAA $ 15 0002 97 15 LDAA # $ 08 0004 86 08 ADDA $ 15 0006 9B 15 WAI 0008 3E

  12. Extended Addressing Mode • The extended addressing mode becomes indispensable when memory locations beyond the zero page must be addressed. Here, as always, an example is worth a thousand words: • LDAA $$ 3C5E Load A from memory 3C5E • Op-codes B6 3C 5E

  13. Three Trick Questions • What is the outcome of B6 00 2A ? • What is the outcome of LDAA # $ 3C5E ? • What is the outcome of STAB $$ 3C44 ?

  14. Trick Questions . . . Answered! • What is the outcome of B6 00 2A ? Legal but not very smart. • What is the outcome of LDAA # $ 3C5E ? Not Legal • What is the outcome of STAB $$ 3C44 ? O.K. and op-code is F7 3C 44

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