DigicoolThings Forum

Many months ago I started collecting Motorola 6800 series chips from old telephone linecards that were being E-wasted. I've come into possession of many 2MHz rated versions of the 6800, 6821, 6840, and 6850.
I wanted to see if there was something I could do with these chips. I searched the Internet for 6809/6309 homebrews and found the MECB standard. I really like some of the design choices, i.e. using PLDs for address decoding.
I also love UNIX systems and want to run FUZIX on my 6309 computer. FUZIX requires at least 64K RAM to run on a 6809/6309, which means we'll need an MMU like the 6829 to page RAM in and out of memory space.
All this means I'll have to modify the existing MECB 6809/6309 card and break out RAM+MMU to a separate card. And I don't have previous hardware design experience. But hopefully I can learn with this project

Let me know what you think and how you would move forward with such a thing

Hi. Welcome to the Forum!

This sounds like a really interesting project.

I’ve actually not come across FUZIX before, but a quick read tells me I’m interested to know more.

It indeed does sound like a seperate banked memory card would be the best solution for supporting larger banked memory models, allowing support for more powerful operating systems (perhaps NitrOS9 as well).

We’d just need to pull the memory chips (RAM & ROM) from the CPU Card, and plug in the alternative MMU / Banked Memory Card.

All that is needed is an appropriate banked memory design. Ideally one that can be configured to support different CPU’s (if practical).

I look forward to hearing more, and perhaps helping out (where I can).

Greetings luRaichu, I am looking into the possibilities of making an MECB simple memory manager using PLD to do the support logic together with latches for the address bus lines. I haven't got very far yet having to learn PLD design as part of the process. I have heard of the 6829 but I was led to believe they were never mass produced and may be hard to obtain. I am looking at other memory manager designs used for both 6809 and Z80 systems, something to run RomWBW CP/M would be a good staging post for me as I have a working system on another bus standard. For 6809 I think Flex will be my choice to emulate an SWTP 6809 system. Best regards, David

djrm wrote: Wed Aug 20, 2025 7:02 am Greetings luRaichu, I am looking into the possibilities of making an MECB simple memory manager using PLD to do the support logic together with latches for the address bus lines. I haven't got very far yet having to learn PLD design as part of the process. I have heard of the 6829 but I was led to believe they were never mass produced and may be hard to obtain. I am looking at other memory manager designs used for both 6809 and Z80 systems, something to run RomWBW CP/M would be a good staging post for me as I have a working system on another bus standard. For 6809 I think Flex will be my choice to emulate an SWTP 6809 system. Best regards, David

I have made a 6309 card with DAT, used 74ls374 for task latch, 74ls244, 74ls257, gal22v10 and 70ns mmu ram. I tihnk it works ok but yet to get 0s9 running on the card to verfiy all ok.