1. Physics 413 Chapter 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 A
WAI Stop (Wait)

5. Op-codes Assembly Language Memory Location Op-codes CLRA 0000 4F
INCA C
WAI E

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

7. Object Code Program # 2
Assembly Language Memory Location Op-codes
LDAA # $
ADDA # $ B
WAI E

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 # $ Load 12
op-code
Direct LDAA $ Load from memory 0012
op-code

10. My Third Program Assembly Language Memory Location Op-codes
LDAA # $ 04
STAA $ 15
LDAA # $ 08 ? ?
ADDA $ 15
WAI

11. My Third Program Assembly Language Memory Location Op-codes
LDAA # $
STAA $
LDAA # $
ADDA $ B 15
WAI E

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