NES Emulator Dashboard

Program code

Controls

CPU status

A

--

X

--

Y

--

PC

----

SP

--

STATUS

--------

FETCHED

--

ADDR_ABS

----

ADDR_REL

----

OPCODE

--

CYCLES

----

RAM

What the 6502 is doing

The 6502 is a tiny CPU. It repeatedly: fetches a byte from memory (an instruction), decodes what it means, then executes it.

Key ideas

RAM is just a big list of bytes (00–FF) at addresses (0000–FFFF).
PC (Program Counter) is “where the next instruction lives.”
A is the main working register (“the CPU’s hand”).
Fetch → Decode → Execute happens over several cycles.

This demo program

A9 42 = LDA #$42 → put 42 into A
8D 20 00 = STA $0020 → write A into RAM at $0020
4C 00 00 = JMP $0000 → set PC back to $0000 (loop)

Result: RAM at $0020 becomes 42 and stays that way, while the PC loops forever.

What to watch in the control panel?

PC highlight shows where the CPU is reading next.
OPCODE shows the current instruction byte (like A9 / 8D / 4C).
ADDR_ABS shows the computed memory address (like 0020).
A should become 42 after the first step.