DEV — Development Environment Vehicle
The machine with no processor in it.
Where the CPU socket would be, the DEV board has a Teensy 4.1 running a cycle-accurate 65C02 emulation, wired to a real bus through level shifters. From the rest of the machine's point of view nothing is different — the same signals appear on the same pins at the same times.
What you gain is control. Four buttons on the board:
- Run/Stop — halt the processor mid-program, with the bus frozen where it is
- Step — advance one instruction at a time and watch what changes
- Reset
- Frequency — slow the clock right down, or speed it up
Real silicon won't let you do any of that. This board was built to debug the BIOS and the early cards, and it's still the fastest way to find out why something isn't working.
The machine in a browser
Plug the DEV into your network and it announces itself as 6502.local, serving its own web page: the video output, the controls, a debugger, and a keyboard that types into the emulated machine. No cables to the desk at all — you sit at your laptop and the 6502 is somewhere else in the house.
What else is on it
An SD card slot for ROMs, cartridges and programs, USB host for keyboards and Xbox controllers, and a battery-backed clock — all hanging off the Teensy rather than the 6502 bus. There's also a bus connector and a card slot wired up for driving genuine hardware, though nothing in the firmware uses them yet; they're there for anyone who wants to take it further.
The DEV Output Board is a second Teensy driving a 2.4" color LCD, emulating the video and sound chips. The DEV board streams the same audio-visual data over USB at the same time, so a browser can display the output in parallel — which is where the emulator started life.
Where to get it
6502-DEV repository — schematics, board files, and the Teensy firmware. The printable reference sheet is here.
The CPU core is vrEmu6502, which is excellent and worth reading on its own account.
📄 6502-DEV card — the machine on two printable pages. The card index has the rest.