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Emulator for 6809 CPU based system like Dragon 32 / CoCo written in Python...

Project description

Dragon/CoCO emulator written in Python

DragonPy is a Open source (GPL v3 or later) emulator for the 30 years old homecomputer Dragon 32 and Tandy TRS-80 Color Computer (CoCo)…

The MC6809 project is used to emulate the 6809 CPU.

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Dragon 32 with CPython 3 under Linux:

screenshot Dragon 32

Tandy TRS-80 Color Computer 2b with CPython 2 under Windows:

screenshot CoCo under Windows

(Note: Python 2 support was removed)

DragonPy is written in Python. It’s platform independent and runs with Python and PyPy under Linux/Windows/OSX/… It’s tested with Python 3.x, PyPy

DragonPy will not be a second XRoar written in Python. This project is primarily to lean and understand.

Future goals are:

  • Implement a integrated development environment for BASIC programs

A full featured Dragon / CoCo emulator is XRoar.

Current state

The Dragon 32 / 64 and CoCo ROMs works in Text mode. Also the “single board computer” ROMs sbc09, Simple6809 and Multicomp6809 works well.

There is a rudimentary BASIC editor with save/load BASIC programm listings direct into RAM.

Looks like this:

old screenshot BASIC Editor (older version of the editor)


The Vectrex (Wikipedia) is a vector display-based video game console. The Hardware are only the 6809 CPU, a 6522 Versatile Interface Adapter and the AY-3-8912 sound chip.

Current state is completely not usable. The 6522 is only a dummy implementation. It makes only sense to display some trace lines, e.g.:

.../DragonPy$ poetry run DragonPy --verbosity 0 --machine=Vectrex run --trace --max_ops=1

BASIC Editor

Use “BASIC editor / open” in the main menu to open the editor.

You can load/save ASCII .bas files from you local drive or just type a BASIC listing ;) With “inject into DragonPy” you send the current listing from the Editor to the Emulator and with “load from DragonPy” back from emulator to editor. Note: The is currently no “warning” that un-saved content will be “overwritten” and there is no “auto-backup” ;)

The “renumbering” tool can be found in the editor window under “tools”

You can also run the BASIC Editor without the Emulator:

.../DragonPy$ make editor
# or:
.../DragonPy$ poetry run DragonPy editor

A rudimentary BASIC source code highlighting is available and looks like this:

screenshot BASIC Editor

Special feature: The Line number that are used in GOTO, SOGUB etc. are extra marked on the left side.


IMPORTANT: The PyPi package name is DragonPyEmulator and not only “DragonPy”!!!

pip install DragonPyEmulator

from source

~$ git clone
~$ cd DragonPy/
~/DragonPy$ make
help                 List all commands
install-poetry       install or update poetry
install              install DragonPy via poetry
update               Update the dependencies as according to the pyproject.toml file
lint                 Run code formatters and linter
fix-code-style       Fix code formatting
tox-listenvs         List all tox test environments
tox                  Run pytest via tox with all environments
tox-py36             Run pytest via tox with *python v3.6*
tox-py37             Run pytest via tox with *python v3.7*
tox-py38             Run pytest via tox with *python v3.8*
pytest               Run pytest
update-rst-readme    update README.rst from README.creole
publish              Release new version to PyPi
download-roms        Download/Test only ROM files
profile              Profile the MC6809 emulation benchmark
benchmark            Run MC6809 emulation benchmark
editor               Run only the BASIC editor
Vectrex              Run GUI with Vectrex emulation (not working, yet!)
sbc09                Run GUI with sbc09 ROM emulation
Multicomp6809        Run GUI with Multicomp6809 ROM emulation
Simple6809           Run GUI with Simple6809 ROM emulation
CoCo2b               Run GUI with CoCo 2b emulation
Dragon32             Run GUI with Dragon 32 emulation
Dragon64             Run GUI with Dragon 64 emulation
run                  *Run the DragonPy Emulator GUI*

~/DragonPy$ make install-poetry
~/DragonPy$ make install
~/DragonPy$ make run

# use the CLI:
~/DragonPy$ poetry run DragonPy --help
~/DragonPy$ poetry run DragonPy

install in virtualenv by foot:


# Create virtualenv:
.../$ python3 -Im venv DragonPy

# activate created virtualenv:
.../$ cd DragonPy
.../DragonPy$ source bin/activate

# update pip before install:
(DragonPy) .../DragonPy$ pip install -U pip

# Install DragonPy:
(DragonPy) .../DragonPy$ pip install DragonPyEmulator
Collecting DragonPyEmulator
Installing collected packages: click, six, dragonlib, pygments, MC6809, DragonPyEmulator
Successfully installed DragonPyEmulator-0.5.3 MC6809-0.5.0 click-6.7 dragonlib-0.1.7 pygments-2.2.0 six-1.11.0

# start Emulator
(DragonPy) .../DragonPy$ DragonPy


There are several ways to install the project under windows.

The following is hopeful the easiest one:

The default boot_dragonpy.cmd will install via Python Package Index (PyPi) into %APPDATA%\DragonPy_env

start DragonPy

The is a simple “starter GUI”, just call the cli without arguments:


It looks like this:

starter GUI


All needed ROM files, will be downloaded automatically.

The files will be downloaded from:

Dragon 32 + 64
CoCo 2b

sbc09 and vectrex ROMs are included.

All ROM files and download will be checked by SHA1 value, before use.

run tests

You can run tests with PyPy, Python 2 and Python 3:

~/DragonPy$ make pytest
# or:
~/DragonPy$ make tox
# or:
~/DragonPy$ poetry run pytest

more screenshots

“sbc09” ROM in Tkinter window:

screenshot sbc09

“Simple6809” ROM in Tkinter window:

screenshot simple6809

Dragon Keyboard

The keyboard mapping is stored into dragonpy/Dragon32/

Some notes:

  • “CLEAR” is mapped to “Home” / “Pos 1” key
  • “BREAK” is mapped to “Escape” button
  • “LEFT” is mapped to left cursor key and to normal backspace, too.

A “auto shift” mode is implemented. So normal lowercase letters would be automaticly converted to uppercase letters.

paste clipboard

It is possible to paste the content of the clipboard as user input in the machine. Just copy (Ctrl-C) the follow content:

10 CLS
20 FOR I = 0 TO 255:
30 POKE 1024+(I*2),I
50 I$ = INKEY$:IF I$="" THEN 50

Focus the DragonPy window and use Ctrl-V to paste the content.

Looks like:

Then just RUN and then it looks like this:

DragonPy schematic

+------------------+                         +---------------------+
|                  |                         |                     |
| +-------------+  |                         |       6809 CPU      |
| |             |  |                         |       +     ^       |
| |     GUI     |  |                         |       |     |       |
| |             |  | Display RAM callback    |    +--v-----+--+    |
| |  .--------------------------------------------+   Memory  |    |
| |  |          |  |                         |    +--+-----^--+    |
| |  |          |  |                         |       |     |       |
| |  |          |  |                         | +-----v-----+-----+ |
| |  |          |  |                         | |    Periphery    | |
| |  |          |  |     Keyboard queue      | |   MC6883 SAM    | |
| |  |          +--------------------------------->MC6821 PIA    | |
| |  |          |  |                         | |                 | |
| +--+-----^----+  |                         | |                 | |
|    |     |       |                         | +-----------------+ |
|    |     |       |                         |                     |
| +--v-----+----+  |                         |                     |
| |             |  |                         |                     |
| |   Display   |  |                         |                     |
| |             |  |                         |                     |
| +-------------+  |                         |                     |
+------------------+                         +---------------------+


The current implementation is not really optimized.

With CPython there is round about 490.000 CPU cycles/sec. in console version. This is half as fast as the real Hardware.

With PyPy round about 6.900.000 - 8.000.000 CPU cycles/sec. In other words with PyPy it’s 8 times faster as the real Hardware.

e.g. The Dragon 32 6809 machine with a 14.31818 MHz crystal runs with: 0,895MHz (14,31818Mhz/16=0,895MHz) in other words: 895.000 CPU-cycles/sec.


  1. implement more Dragon 32 periphery

missing 6809 unittests after coverage run:

  • MUL
  • BVS


Some Python/BASIC tools/scripts around Dragon32/64 / CoCo homecomputer.

All script are copyleft 2013-2020 by Jens Diemer and license unter GNU GPL v3 or above, see LICENSE for more details.

Python scripts:

BASIC programms:

Input/Output Tests

/BASIC/InputOutput/keyboard.bas Display memory Locations $0152 - $0159 (Keyboard matrix state table)

Example screenshow with the “Y” key is pressed down. You see that this is saved in $0153:

KeyBoard Screenshot 01

Example with “U” is hold down:

KeyBoard Screenshot 02


Some code based on:


An Apple ][ emulator in Python

XRoar A really cool Dragon / CoCo emulator

included Python modules:

python-pager Page output and find dimensions of console. Motorola S-Record utilities


dragonlib Dragon/CoCO Python Library

MC6809 Implementation of the MC6809 CPU in Python

pygments generic syntax highlighter



Note: this file is generated from README.creole 2020-10-01 13:19:41 with "python-creole"

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