COE538 Assembly Basics Cheat Sheet

Instruction Abbreviations

• LDAA → LoaD Accumulator A
  • Example: LDAA #55 → Load A with 55
• LDAB → LoaD Accumulator B
• ADDA → ADd to Accumulator A
  • Example: ADDA $20 → A = A + value at memory address $20
• SUBA → SUBtract from Accumulator A
• STAA → STore Accumulator A into memory
• TFR → TRansFeR between registers
• EXG → EXchanGe registers
• INCA → INCrement A → A = A + 1
• NOP → No OPeration (do nothing)

Special Symbols

• # → Immediate Value

  • Means: "Use this number directly, not from memory."
  • Example: LDAA #55 → A = 55

• $ → Hexadecimal Number

  • Means: "The following number is in hexadecimal."
  • Example: LDAA $20 → A = value stored at memory[0x20]

• @ → Indirect Addressing (pointer)

  • Means: "Use the memory location stored in a register or memory cell."
  • Example: LDAA @X → A = memory[X]

C Language Analogy

• LDAA #55 → A = 55;
• LDAA $20 → A = memory[0x20];
• LDAA @X → A = memory[X];

CCR (Condition Code Register) Flags

• C (Carry): Unsigned overflow → e.g. 255 + 1 = 0 with C = 1
• V (Overflow): Signed overflow → e.g. 127 + 1 = -128 with V = 1
• Z (Zero): Result is zero
• N (Negative): Result is negative (most significant bit = 1)