| uClinux running on a 68008 board [message #7477] |
Thu, 09 April 2020 14:08  |
computerdoc
Messages: 130
Registered: October 2015
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Senior Member |
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Hi 68K Enthusiasts!
Encouraged by a fellow member, I am sharing about building a 68008 SBC called 68Katy! This is the url:
https://www.bigmessowires.com/68-katy/
I found this project sometime in the last 10 years. I have been wanting to build a 68008 board for most of the last 10 years, but I needed to either come up with a design or share someone else's design. While studying the 68Katy web page, I noticed 1 glaring problem. I didn't know how to solder surface mount devices! I have recently become more interested in learning the fine art of soldering SMDs so I began to study how other people have done it including Plasmo. I think I am ready to take the plunge and get my SMD soldering feet wet! Fortunately, the 68Katy only has 1 SMD! This SMD is a CPLD with legs very close together, well for me anyway. After studying other SBC builders on Youtube, I have decided I will try using solder paste and use the kitchen oven to solder the SMD on to the board.
I downloaded all the files and sent in the gerbers to jlcpcb.com. While I waited for the boards to arrive, I studied the 68Katy web site very carefully to make sure I understood everything the designer and builder of this board said. Having not built a board in over 2 years since my family moved to NC and not having a place to work, I finally figured out how I was going to proceed creating a workspace for my PCB building. That is an account all to itself which I will not bore you with. Suffice it to say I now have a place and a table to work on. Whoo-Hoo!
Once I received the boards from jlcpcb.com, I looked over the boards carefully for any problems. After not finding any problems with the PCB, I started populating the board with parts I had on-hand to see what parts beside the CPLD I was going to need to order. I made my list and ordered the needed parts for this board and another board that is on building hold due to needed parts I don't have for that board as well. Out went the order to a couple of places and now my 68Katy board is on building hold as well.
Since I used his gerbers, my board with look much the same as his except for 1 particularly interesting point! The Sparkfun USB to 8-bit Parallel port module has been discontinued! Eegads! What am I going to do now? I needed to come up with another way to add a USB port to this board without the Sparkfun board. Hmmm... My gears start spinning for a while, like days and weeks until I hit upon a couple of ideas I had been tossing around in my mind. The first idea is to make a board to adapt my FTDI USB to Parallel board to the Sparkfun's USB to Parallel module's foot print since it uses the same chip. The 2nd idea is to look for a schematic for the Sparkfun USB to parallel board. Lo and behold, the ad for the Sparkfun board has not only pictures, but a schematic and eagle files as well. I think I'll choose making a copy of the Sparkfun board! I was going to use though-hole parts for everything I could, but to ensure the board worked the 1st time, I decided to use Sparkfun's layout of their board.
This brings me up to the present. I have the eagle files for the original Sparkfun board inserted into my eagle program but I have not had the board fabricated yet. As yet not conquering the SMD soldering hump in my abilities, I'm not quite sure how to order the correct parts for the SMDs for that board so I am going to have to ask for some help deciding how to choose the correct footprint parts for this Sparkfun duplicate board as I haven't found a BOM - Bill of Materials yet.
Now for a couple of pictures. The designer and creator the 68Katy's board looks like this:
My board currently looks like this so far:
Well, here it is! I can't seem to flip the picture around so that it is oriented in the same direction as the original 68Katy. Other than that, my 68Katy is pretty much identical except for the different color LEDs.
Please let me know what you think of this board and its possible applications. Please do be kind as most of us are still learning! 
Your fellow SBC builder,
Kip
Kip Koon
computerdoc at sc dot rr dot com
http://www.cocopedia.com/wiki/index.php/User:Computerdoc
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| Re: uClinux running on a 68008 board [message #7534 is a reply to message #7532] |
Wed, 15 April 2020 08:16  |
Yves-D.
Messages: 21
Registered: January 2020
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Junior Member |
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@Just4Fun: You're welcome. Your projects are highly interesting and innovative to me. I keep an eye on to your progress with the V20-MBC and will do so if you embark on an 68k project.
It changes a bit from the predominant Z80 projects, of which i have my share sitting around on my desk. The nice design of the 68k CPU is a lot more straightforward than the Z80...but you can't say that aloud around here ;-)
PS: If you're going to be bus-fiddling on the 68000 execution cycle with an Atmel as co-processor, pay attention to the fact that every 68k had some instruction prefetch.
Even if it appeared officially in the datasheets with the 68010, the basic 68000 also did it, see here: https://community.nxp.com/thread/357766
Unexpected instruction prefetch might blow up your bus control logic.
While I've seen the instruction prefetch with the logic analyzer on a working 68020, I've yet to confirm it on an 68EC000 when my homebrewn board is working.
Yves
[Updated on: Wed, 15 April 2020 08:28] Report message to a moderator |
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