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I can't see any reason at all why you would want to build a 68k based computer now.
I can remember pondering the details of a 68008 (an 8 bit bus version) design in 1982 on a walk in the Derbyshire Peak district.
But 36 years later it won't fly - you'll need 5V logic and memories which are hard to get and the end result will be big, use lots of power and have less welly than an ARM M0 (it should just about beat a basic Arduino).
You can approach it in the same spirit as people do with steam engines.
You can buy 68k based computers easily enough - I have a huge HP thing bought for £5 from an equipment auction - it has a CRT and still boots up.
If you are in the UK you can have it, else it'll be much cheaper to buy one locally.
This would give you all the fun of playing with the 68k but spare you having to spend a fortune on obsolete bits.
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I've been looking into this a bit and have found a few people who have done it recently. One guy built a 68000 computer on a bread board in his spare time in 6 days. Reading his blog post, talking about how interfacing to the 68K is child's-play. I found 16Mhz 68K chips on ebay for $4. 5Volt TTL logic chips are still produced, as well as an assortment of peripherals, like 555 timers. From what I gather it should be a very cheap and possibly simple thing to do. I understand that this will not be a very powerful computer, but like your steam engine example, the fun will be in making it work.
From a practical standpoint you are correct, as the 68K family is well out of date.
However, the whole idea came from an "itch". I've also caught the retro computer bug recently, and found that there are quite a few of us out there (just check out the Z80 google users group). Even though they are in the decline, there are plenty of 5V parts out there and are available from Digi-Key, Newark, Jameco, and host of surplus stores. The prices are still reasonable.
Building a computer from scratch is very educational, and it is satisfying bringing old technology back to life.
Good luck to you Martin!
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Unfortunately I don't have a schematic, but another option which has the fun of making a computer from a microprocessor, and similar instruction set, but using more modern parts and lower voltages, could be to use one of the other Freescale processors that were based on the 68k. For example the ColdFire range has processors to which you can attach RAM and Flash. It would be easier than the 68k in some ways, with the more modern parts (although even ColdFire is old, but still manufactured) - for example even the Palm handheld PDAs of the 1990's, which also had a 68k-compatible chip (the Freescale Dragonball) literally only needed two additional chips, the SRAM and Flash, and zero glue logic. I had fun building a Palm-type device using that chip.
ColdFire has hand-solderable options (QFP package).
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That sounds very interesting. I have heard of this chip while doing research for my build. It sounds interesting. What would be the equivalent of an EPROM in that type of system?
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That would be a Flash chip, something like this:
A lot cheaper than EPROM/EEPROM.
In order to get the initial code in there, there may be existing tools, or you may need to write a small bootloader (e.g. in Assembler code) to accept your executable say over a serial line, and program it into the Flash.
I have got an itch to build a 68000 bases computer. It's been a long time since I've dabbled in this sort of thing. In 1991 I build a 6809 based computer for school. At the time I remember looking into the 68000 and how cool it was and seemed to be a wonder to program on, even compared to the wonderful 6809, and made X86 programming look like Egyptian hieroglyphs. I am looking for a good schematic to base my computer off of. Like I said it's been a while since I've done this sort of thing and I would like to start with a known working system and modify it from there. Is this the right place to ask this sort of question? If not is there a better place?
Thanks in advance,