Overview
The 6502-DEV (Development Environment Vehicle) is the emulation-based member of A.C. Wright's AC6502 family. Instead of a physical 65C02 chip, it runs cycle-accurate 65C02 emulation on a Teensy 4.1 microcontroller, paired with a second Teensy that emulates the video and sound chips. The result behaves exactly like the real hardware but adds developer luxuries: variable clock speed, single-stepping, SD-card loading, USB input, and a built-in web control panel.
History & Design
The DEV exists to make writing and debugging AC6502 software easy. The DEV Board's Teensy 4.1 emulates the CPU (via vrEmu6502) and handles storage, Ethernet and USB; the DEV Output Board's Teensy 4.0 emulates a TMS9918A video chip and a MOS 6581 SID, driven in real time over a high-speed serial link. Hardware buttons give run/stop, single-step, reset and clock-frequency control — turning an invisible CPU into something you can pause and inspect.
System Specifications
| CPU | Emulated 65C02 on Teensy 4.1 (vrEmu6502) |
| Clock | Variable, single-step to multi-MHz |
| Memory | Standard AC6502 map (32KB RAM + ROM + banking) |
| Video | Emulated TMS9918A on 2.4" ILI9341 TFT |
| Audio | Emulated MOS 6581 SID (3 voices, ADSR) |
| Storage | SD card — ROMs, carts, programs, snapshots |
| Network | Ethernet + mDNS, web UI at 6502.local |
| Input | USB keyboard + Xbox 360/One controllers |
| Serial | Terminal interface @ 115200 baud |
| Controls | Run/Stop, Step, Reset, Frequency buttons |
At the machine
The DEV is the developer's workbench of the family — the only one whose CPU you can pause and single-step. Use the front-panel buttons to stop the processor mid-program and step through one instruction at a time, or spin the clock up and down to watch programs speed up and slow down.
The AC6502 Family
| System | Role |
|---|
| DEV | Emulation-based development system (this machine) |
| ACE | All-in-one single-board computer |
| COB | Modular backplane desktop |
| KIM | Keypad + LCD add-on that turns an ACE into a KIM-1 |
| VCS | Cartridge-based game console |
Because the DEV is cycle-accurate, software debugged here runs identically on the real-silicon ACE and COB.
Memory Map
| Range | Contents |
|---|
| $0000–$07FF | Zero page, stack, input & system variables |
| $0800–$7FFF | Program / BASIC RAM (30 KB) |
| $8000–$9FFF | I/O hardware (emulated devices) |
| $A000–$B7FF | Kernal + jump table |
| $B800–$BFFF | Character set ROM |
| $C000–$EDFF | BASIC interpreter |
| $EE00–$FEFF | Machine-code Monitor |
| $FF00–$FFF9 | Wozmon (mini monitor) |
| $FFFA–$FFFF | CPU vectors (NMI, RESET, IRQ) |
Did You Know?
There is no 6502 chip inside — a 600 MHz Teensy 4.1 pretends to be a 1 MHz 65C02, cycle for cycle.
A second Teensy emulates both the TMS9918A video chip and the 6581 SID sound chip at the same time.