Easy 6502 alternative: from 6502 assembly to a CPU you build
Easy 6502 by Nick Morgan is a free tiny ebook on 6502 assembly language (CC BY 4.0) with a JavaScript 6502 assembler and simulator built into the page. Each chapter, from your first program through registers and flags, branching, addressing modes, the stack and jumping to writing a small game, has example programs you can edit, assemble and run, with a debugger that shows the registers and flags and a monitor for memory. Memory from $200 to $5ff is a small pixel screen. The original repository is in maintenance-only mode, and active forks carry it on. Easy 6502 teaches you to program a classic 8-bit processor; digiwleea has you build a simple 8-bit processor yourself, gate by gate.
What Easy 6502 is good at
The friendliest first hour of assembly language there is: short chapters, a real historical processor (the chip in the Apple II, the Commodore 64 and the NES, as the book notes), and a runnable example in every section, ending with a small game on its pixel screen. (digiwleea is an independent project, not affiliated with Easy 6502 or its author.)
How digiwleea is different
digiwleea does not run 6502 code; it shows what an 8-bit processor is made of. In the browser you build NOT and NAND from CMOS transistors, then adders, an ALU, registers, RAM, a program counter and a control unit, through a 40+ level course where every part is checked against its truth table, with an AI tutor (Wleea). The CPU you finish with is an 8-bit accumulator machine, like the 6502's accumulator-centred design but far smaller, whose capstone runs a stored LOAD, ADD, STORE, HALT program. To see a real 6502 at the transistor level, see our Visual 6502 comparison.
| Easy 6502 | digiwleea | |
|---|---|---|
| Focus | Learning 6502 assembly | Digital logic from transistors to a simple CPU |
| The CPU | A simulated 6502 | Built by you: an 8-bit accumulator machine |
| Format | A short ebook with runnable examples | A guided 40+ level course and a lab |
| Runs on | Any browser | Any browser |
| Price | Free, CC BY 4.0 | Free lab and Act I; Premium for the full course |
The same addition on both machines
Add 5 and 10 and store the sum. On the left, 6502 assembly we ran in Easy 6502's simulator on 2026-10-31: it stops with A=$0f (15). On the right, the program of digiwleea's capstone CPU, which the simulator runs to an accumulator of 15 and a stored 15. The 6502 needs CLC because ADC also adds the carry flag.
| 6502 (Easy 6502) | digiwleea capstone CPU |
|---|---|
LDA #$05 | LOAD 14 (memory 14 holds 5) |
CLC | |
ADC #$0A | ADD 15 (memory 15 holds 10) |
STA $00 | STORE 13 |
BRK | HALT |
No sign-up is needed to start: open the lab and place your first transistor, or read the free theory course. The account (and the AI tutor) are optional.
More comparisons: CPU and assembly simulators
See for yourself: build a logic gate from transistors in the simulator, then follow the path from sand to an 8-bit CPU.
Open the digiwleea lab →Frequently asked
What is Easy 6502?
A free online tutorial by Nick Morgan on 6502 assembly language, with a JavaScript 6502 assembler and simulator built into the page so every example can be edited and run.
Why does 6502 addition need CLC?
Because ADC adds the operand and the carry flag to the accumulator. Clearing the carry first with CLC makes it a plain addition.
Can I build an 8-bit CPU myself?
Yes, a simple one: digiwleea's browser course has you build an 8-bit accumulator CPU from transistors up, through gates, adders, registers, RAM and a control unit.