an 6809 system with expansion bus

Similar projects worth following
This is the successor of the Scrumpel8b. It has more RAM and I/O in unused part of the ROM.
In stead of glue logic a gal22v10 is used. All software for Scrumpel8a/b could be used for this Scrumpel with a small modification of the PPORT and ACIA addresses. These need to be changed into $CF20 (PPORT) and $CF00 (ACIA). The gerbers and schematic diagram can be found at github.

This version is expandable and has the following specs:

  1. 48 Kbytes RAM $0000-$BFFF
  2. 16 Kbytes ROM $C000-$FFFF *
  3. 256 Bytes I/O
  4. One serial port 115200 Baud 8N1
  5. On  board 8 bits Parallel I/O port

On the bus two extra addresses for I/O are predecoded.

On board I/O

  • Serial ACIA 68B50 $CF00
  • Paralllel I/O $CF20

*IOSEL is active from $CF00-$CFFF


  • CSAUX $CF60
  • CSPIA $CF40

For other info look at Scrumpel8a/8b project.

Here an example screen output of my dos09 operating system for the 6809

The OS is running in 16K RAM from $8000 to $BE00 and knows only one disk of 1.3 MB.


A foto of the CF card used in Scrumpel8d

JPEG Image - 1.07 MB - 07/18/2022 at 12:11



A dump of my cf-card on scrumpel8d

Portable Network Graphics (PNG) - 130.54 kB - 03/09/2022 at 19:25



Schematic of the CPU board

Adobe Portable Document Format - 170.72 kB - 02/25/2022 at 14:10



The bus connector description.

plain - 449.00 bytes - 01/12/2022 at 06:49


  • 1 × CPU 68B09E CPU
  • 1 × 74HCT73 Logic ICs / Flip-Flops, Latches, Registers
  • 1 × 68B50 ACIA
  • 1 × ATF22V10 6809addresdecoder
  • 2 × 74HCT32 Electronic Components / Misc. Electronic Components

View all 24 components

  • 1
    Positioning of the LEDS POWER, RESET, TXD, RXD and RUN

    The square pad on the PCB indicates the Cathode side of the LED. Long leg of LED is the Anode.

View all instructions

Enjoy this project?



Nick Brok wrote 03/20/2022 at 05:43 point

Unfortunately no one could help me with some FAT Filesystem Code in 6809 assembly. (I found some, but those where written in C.) I've written a simple OS on my own. Because of the less memory I have for the OS (16KBytes of RAM 32K for program-space) it's using only one slice of the CF-card. In that slice I can place 1,3MB of data. I use big buffers for file allocation (2560 sectors) and the root directory (8 sectors). The OS can be used, but it's not earning any prizes. :-(

  Are you sure? yes | no

Peabody1929 wrote 03/19/2022 at 19:10 point

Tell me more!  

  Are you sure? yes | no

Nick Brok wrote 03/05/2022 at 18:52 point

Just received my IDE adapter for Scrumpel8d. It works!

  Are you sure? yes | no

Similar Projects

Does this project spark your interest?

Become a member to follow this project and never miss any updates