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cbmeeks

68K (no Mac) Designs OK?

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I'm sorry if I am way OT here.

 

Last year, I designed a 65C02 computer and had some boards made.  It worked very well and I was very happy.

My next move was to design his 16-bit big brother using a 65C816.  Seemed like a logical choice (still is, really).

 

However, there was something pulling me towards the 68K.  Mainly because I was a hard-core Amiga 500 user in the day.  And, about 20 years ago, I started collecting classic Macs (I have several 68K series Macs).

 

So I decided to byte the bullet (notice a play on words there) and design my first 68K based computer.

It is heavily inspired on the original 128K Mac.

 

But here's my issue...I need a place to bounce questions around and get advice on my design.  I don't see many 68K forums online that aren't focused on a platform like the Mac or Amiga.  My computer will be neither of them (but pull inspiration from them both in some areas).

 

Am I in the right place?  Or, is there somewhere else I should visit?

 

Thanks!

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I would love to hear more on that.

Got your thoughts/ideas/design/whatever you got so far documented somewhere in a blog or something like that?

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If you find a better place, please let us know.   This place it okay for that discussion, but I think you'll get many interested audience and not too many active contributers.   Big Mess 'o Wires did some similar work years back, I think.

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Very interested in your project, what machines besides Mac and Amiga were in the 68000 family, workstations of any kind?

 

We've got Lisa on the 68000 list, it seems someone has streamlined the logic board's design and produced(?) compatible replacement boards:

http://vintagemicros.com/catalog/lisa-board-from-sapient-technologies-p-296.html

 

Curious about your OS choice/development plans?

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Thanks everyone for the interest.  I don't have a blog yet.  But I really should start one.  I really like the format that BMOW does with his projects.  I might follow something similar.

 

I'll either post my progress here (if no one objects) or just post a link to my eventual blog.

 

In the meantime, I gathered up parts that I already have on-hand.  My dream is to design a "Mac like" computer that would fit between the Mac 512K and Amiga 500.  Closer to the Mac because the Amiga had advanced chips for it's day and I'm a HDL newbie.

 

I will be wire-wrapping my first prototype starting this weekend.  The CPU of choice is a 68SEC000.  I have bought a TQFP-64 to DIP converter so I got some soldering to do.  The final design will likely use a "largish" FPGA and maybe some smaller CPLD's.  I don't want to go insane on the FPGA choice.  Mainly because my eyesight restricts me to soldering TQFP-100 to MAYBE -144 packages.  I have no interest in BGA.

 

So, what do I actually have right now?

 

Almost everything.  However, they are a mixture of small boards, slower parts, etc.  So not the final specs.  For example, I will be using two SRAM chips for 16 bit memory that run 55ns.  BUT, my final design will incorporate 16-bit SRAM at 8-10ns with 1 MiB minimum.  I thought about getting DRAM chips because they are very cheap and 16 MiB would cost almost nothing.  But, I don't want the extra hassle of DRAM refreshes and column/row logic.  Plus, no affordable computer in 1984 - 1986 had 16 MiB anyway.  1-2 MiB for my final design sounds good and the 16-bit SRAM chips are not that expensive.

 

On my CPU adapter, I have a small bag of wire-wrap pins that I will have to painstakingly solder one by one so that the adapter board can be used with wire wrap.  Not to mention the small SMD CPU itself.  :-)

 

Anyway, my parts so far are (for prototype):

 

68SEC000 CPU (with adapter)

512 KiB SRAM 55ns x 2  (used for odd/even) memory.  1 MiB total RAM.

128 KiB ROM 70ns NOR flash x 2 (used for odd/even) memory.  256 KiB total ROM.

DUART Serial (2 ports) via NXP 28L92.

ATF1504 CPLD (32 I/O)

ATF1508 CPLD (64 I/O) - 7.5ns

TinyFPGA A2 (~21 I/O)

TingyFPGA BX (~41 I/O)

Parallax Propeller MCU (8 cores, 32 I/O).  Possibly used for audio (has great SID emulation) and/or general I/O for keyboard/mouse, SD, etc.

 

Eventual specs for final design:

1-2 MiB RAM

256 KiB ROM

SD card running FAT16

USB mouse/KB (MAYBE PS/2 if USB proves to be a headache).

640 x 480 VGA.

I don't want SVGA, massive sprites, etc.  I'm leaning more towards a simple frame buffer with possibly hardware blitter. 

For colors, I'd like to shoot for at least 256 (8-bit). 

I'm undecided if I want to force a static display (like the original Macs) or allow a more dynamic display like the Amiga (and later Macs).

Sound.  (duh..lol).  SID emulation sounds good...but I probably won't use it.  If you have memory, then audio buffers and DAC's sound so much better.  Just compare the Amiga against the C64.  The IIgs should be noted because of the massive number of channels...but still, sampled audio will probably be the way to go.

 

Right now, most things are up in the air.

 

More than likely, I will use the ATF1508 CPLD as a simple VGA controller and MMU.  Mainly because it has the most pins.  But I'm sure I will find something to do with those other PLD devices.

 

If/When I finish my final design, I hope to have a smallish 4 layer board made.  Which I will make available. 

 

If this is successful...if I love working on it after all of that....and people still want it....I might look into a second revision where the 68K is handled within an FPGA.  Not true "retro", but much easier to sell and source.

 

Any questions, just ask...

 

Wish me luck!!

 

PS, I still haven't thought of a name yet.  I want something catchy but not cheesy.  One thing I like about "Macintosh" is that it sounds good...looks good...and can be shortened to "Mac".  Plus, it falls inline with "Apple".  It would be hard to beat that.  :-D

 

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16 hours ago, Trash80toHP_Mini said:

Very interested in your project, what machines besides Mac and Amiga were in the 68000 family, workstations of any kind?

 

 

The very early Sun machines were 68000

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1 hour ago, ScutBoy said:

The very early Sun machines were 68000

The little known Unix based MassComp Mini Computer used two 68000s; one for the CPU and one to support its advanced graphics.   We had a number of them at NASA JSC in the mid-80s.

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Small update...

 

This weekend was unproductive.  I had FOUR large deployments (for my real job) that took up most of my weekend.

 

I did manage to solder the small QFP-64 68SEC000 to a breakout board.  This breakout board will next get 64 wire-wrap pins soldered to it so that I can use it.

Next after that is free-running it.

 

Someone asked what OS.  Well, at first, I *might* try uLinux just to get it running.  But my goal is to develop my own OS.  But that is a tall order.

Either way, I will keep people posted.

 

Thanks.

 

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On 7/11/2019 at 3:59 PM, Trash80toHP_Mini said:

what machines besides Mac and Amiga were in the 68000 family, workstations of any kind?

I had a Sinclair QL, which was quite a fun little machine based on the m68008. Of course, there's the Atari ST, the Japanese LUNA machines, Sony's NET WORK STATION workstations, NeXT, of course, Sharp's X68000/X68030 series, Hewlett Packard's 9000 Series 300 and 400 workstations, Suns, Apollos, plus lots of VME boards, including multiprocessor systems. Let's not forget the Tandy TRS-80 Model 16 and Tandy 6000! There were plenty of others I'm not remembering right now.

 

I'd love to build a simple system some time using either the 22 address bit version of the m68008, or perhaps an m68030 since it can size its bus to 8 or 16 bits, plus it can run Unix / BSD without extra chips because it has an MMU. One day!

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Another forum to check out is RetroBrew computers at https://www.retrobrewcomputers.org/forum/index.php

 

That forum and its wiki are all about doing homebrew computer designs with retro CPUs (68K, Z80, etc).

 

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On 7/12/2019 at 7:58 AM, cbmeeks said:

BUT, my final design will incorporate 16-bit SRAM at 8-10ns with 1 MiB minimum.

Are you planning to share RAM between the CPU and the framebuffer? Because if not I suspect the 55ns RAM will be plenty fast for a 68000. (I assume you're using AS6C4008s for now?)

 

Not that larger 10ns SRAMs are prohibitively expensive or anything. the AS6C4008 just happens to be really popular for homebrew because it's still available in a standard DIP package.

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