68KatyClone

An open-hardware design for an 8-bit Motorola 68008 system. Please feel free to re-use any of the parts enclosed in this repository, or see the license for the hardware if in doubt. However, the monitor and Linux image are both GNU GPL licensed, so these need care. Since I can't include the modified Linux image files in this repository itself (the file is too large to be included), I'll suffice by pointing you to with a link. This was adapted from the uCLinux original. Ironically, the compiled binary image is small enough to fit into the 512k ROM, of course.

NOTE This is a work in progress, by a guy with no prior experience in CPU board prototyping. Although I'm enjoying myself thoroughly and things are progressing well, this project comes without guarantees.

• Update 17-03-202: I got my first address and data bus readouts today, using an Arduino Mega. It's not making much sense to me yet, but it soon will. It's clear that the processor is executing instructions!
• Update 15-03-2020: There is a working 'single-stepping' and power-up/reset schematic that will serve as the basis for the rest of the project. The rest may or may not work, I'm not done debugging yet.
• Update 22-03-2020: Made a few huge steps forward in having a working board, but I can't get a decent serial readout yet.

Credits

• This repository is my attempt to build a re-vamped edition of Steve "Big Mess-O-Wires" Chamberlin's 68Katy, for which I owe him many thanks. It's my first go at breadboard prototyping, but since I'm learning so much I thought I'd contribute by publishing my findings. It has been quite the ride thus far.
• Also, I'd like to point to Ben Eater's 6502 project, which has been quite inspirational.
• I got myself a scope based on YouTubers Adrians Digital Basement and EEVblog.
• The vid by John Tsiombikas helped me out hugely in putting together the single-stepping part of the board.
• The power-up/reset circuit was based on a design published by Jeff Tranter

I'm using the 68Katy design because it's pretty well documented, as Motorola 68K projects go. There's a lot of people experimenting, I even believe there's some kind of revival going of people baking 8-bit systems just for fun. The fact that a lot of the components can be ordered over the mail very cheaply most certainly adds to the fun - parts are available in abundance and even the shipping is often very cheap if you're willing to wait a couple of weeks. My guess is that these kinds of projects are being undertaken by late-30's to mid-50's guys tinkering away in sheds and attics. I happen to be just one of them.

The reason I wanted to do a 68K project, is because I used to be, and still am, the proud owner of a Texas Instruments TI-92 that I bought in high school. At the time, I thought of it as a marvel of technology. I dabbled unsuccessfully in some C++ coding (I found it too hard), but the TI-92 allowed on-board BASIC programming an fancy graph plotting. So there my journey began. Now, over 20 years later, I'm a professional software developer and I believe I'm now better equipped for taking on the challenge of building an 8-bit system from bare components.

Schematics

The KiCad folder contains a work-in-progress translation of the schematics from Steve Chamberlin, updating it to a more modern version. I'm working on a board but at the moment it's not working. So use at your own peril.

Memory Map

BREADBOARD 68 KATY 00000 - 77FFF : ROM 78000 - 79FFF : serial in
7A000 - 7BFFF : serial out
7C000 - 7DFFF : serial status
7E000 - 7FFFF : LED register
80000 - FFFFF : RAM

Software

ROM image

The ROM folder contains the ROM image: the monitor program and the Linux image. Send it to the ROM using a ROM programmer, I used a TL866II plus

GAL image

The GAL/68katy folder contains the .jed compiled image. Send it to the GAL using a GAL-compatible ROM programmer, I used a TL866II plus For good measure I also included the OpalJR compiler - as the license seems to allow it; I got it from here. There's no reason not to include it here - it's the same program the original 68Katy GAL used to compile so it should be OK, although I can never be 100% sure unless I compare the JEDEC compiled file to the original (which I can't). Since it's a 16-bit DOS program, you need something like DOSBox to run it.