• infinite loop of:
  • fetch → fetch instruction from memory at current PC
  • decode → figure out instruction
  • execute → execute instruction

fetch

• read instruction at PC
• instruction: 2 bytes → two successive reads (or use uint16_t to represent the instruction and read once)
• immediately increment PC
• error prone if incrementing after execute

decode

• read instruction using instruction format
• extract values to opcodes before decoding using #define

execute

• nothing significant here, just execute the behavior through the switch statement (or equivalent)