COMMODORE PET 2001

⚠ RESET VECTOR — How the 6502 Boots

When the PET is powered on or reset, the 6502 CPU reads the Reset Vector from fixed address $FFFC (low byte) and $FFFD (high byte). This is hardwired in silicon — the CPU always fetches its starting Program Counter (PC) from $FFFC/$FFFD.

On the Commodore PET 2001 with BASIC 1.0 ROMs, the reset vector at $FFFC/$FFFD contains $00/$F0, which the CPU combines into the 16-bit address $F000 — the start of the Kernal initialization routine in the "F" ROM (chip UD9, mapped at $F000–$F7FF). This is where execution begins on every boot.

📌 Summary: Power On / Reset → CPU reads PC from $FFFC/$FFFD → Reset vector points to $F000 → Kernal init begins

If the ROM at $F800–$FFFF (UD9 chip) is not loaded, the CPU reads garbage from $FFFC/$FFFD and will execute from a random address — this is authentic PET failure behavior (screen full of garbage).