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Hello from the 68K land

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Plasmo

Experienced Member
Joined
Aug 29, 2017
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New Mexico, USA
Hello, I'm a retired hardware engineering who'd worked on embedded 680x0 products during the 80's and 90's. I want to revisit the 680x0 in my retirement and expand my knowledge to the desktop environments. --Bill
 
Plasmo said:
Are there much interests in homebrew 680x0 computer?
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There is of course. Radio Electronics used to feature a couple of 68k homebrewed units. For instance. My advice though is to select one particular 68k machine and build onto that. I used to have an Apollo 68030 (IIRC) motherboard, which I sold like a fool. It was an extremely simple design, no asics IIRC. It's sort of obscure though. I like Atari and early color Macs (II, IIX, IIFX). I'm staying away from Amigas, how thin can you spread yourself. I certainly don't hate them. But at least the Ataris had 400 lines of resolution in monochrome. The Mac IIs had that and more. But it's not a fair comparison, as the Atari STs were contemporaneous with early compact Macs. The Atari Coldfire project is interesting. If I had the skills of a hardware engineer, I'd personally love to contribute to something like that.

I have this attraction to the Sega Genesis system, I guess ever since I opened one up (I've had several, never seem to be able to hold onto some things). It has a 68k of course. The problem is it has asics. Bad bad, very bad. No way of fixing such a unit once it craps the bed.
 
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Yeah, definitely interested in homebrew or embedded stuff as well (I actually have a nice little Coldfire development board I need to do more with...)
 
Thanks you all for commenting. I wasn't sure whether a homebrew 680x0 is considered "vintage computer" since it is obviously made recently. As a hardware engineer, design, fabricate, test new computers were my regular job. The hard part is keeping the cost down and find useful free software to run on it.
I'm in the process of redesigning Tiny68K, a low-cost (somewhat) 68000 SBC with 16meg memory. I want to design a bare-bone $10 68000 computer, but I wound up offer it as a CP/M68K-ready kit for $20.
https://www.retrobrewcomputers.org/doku.php?id=boards:sbc:tiny68k
 
That Tiny68K 68000 SBC looks pretty cool. I might be interested in something like that.

Is there any room left in the EPM7128 to implement a periodic timer interrupt? Just wondering about maybe running some sort of small preemptive multi-threaded OS.
 
gslick said:
That Tiny68K 68000 SBC looks pretty cool. I might be interested in something like that.

Is there any room left in the EPM7128 to implement a periodic timer interrupt? Just wondering about maybe running some sort of small preemptive multi-threaded OS.
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The 68681 Dual UART already has a 16-bit timer. I program it to generate 100Hz interrupts in the bootstrap monitor.

Part of the redesign was to add a real time clock. CP/M 68K v1.3 does not need time of day, but other OS do. I stumbled across the 16meg memory because it is cheap and a good fit for 68000 but it does open the door for multitasking OS.
 
ClassicHasClass said:
That, too!

Mine's still working great. I need to do more with it.
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If you haven't made the fix to the floppy drive you had better do it before the thing self destructs on you.
Once the head is damaged you will not be able to find an easy replacement.
Referring to the Canon Cat.
Dwight
 
Plasmo said:
The 68681 Dual UART already has a 16-bit timer. I program it to generate 100Hz interrupts in the bootstrap monitor.

Part of the redesign was to add a real time clock. CP/M 68K v1.3 does not need time of day, but other OS do. I stumbled across the 16meg memory because it is cheap and a good fit for 68000 but it does open the door for multitasking OS.
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Oh, I didn't know the 68681 DUART has a built-in timer/counter that can be used. That solves that problem. I briefly used µC/OS-II on a Freescale ColdFire CPU. I haven't tried FreeRTOS on anything yet. I wonder if that could work on a tiny system like this. Might be an interesting learning experience.
 
Trust me I'm not trying to be a party pooper, and I see it as entirely admirable to produce an ultra low cost uC. But what do people do with them. Personally my lean is towards small, full featured boards, ala Ampro or even the aforementioned Sega Genesis. That's the shizzle I love.

But regardless when this project has run it's course, we'll have to bug Bill into designing something with a 68060. Or an fpga with a 68k core. Hello Moto!
 
2icebitn said:
Trust me I'm not trying to be a party pooper, and I see it as entirely admirable to produce an ultra low cost uC. But what do people do with them. Personally my lean is towards small, full featured boards, ala Ampro or even the aforementioned Sega Genesis. That's the shizzle I love.

But regardless when this project has run it's course, we'll have to bug Bill into designing something with a 68060. Or an fpga with a 68k core. Hello Moto!
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I quite agree with you. Even if it is CP/M-68K ready at $10, what can I really do with it? CP/M-68K has so few applications. Within the low-cost pcboard form factor (100mm x 100mm), it is entirely reasonable to add an Ethernet and VGA-class graphic chip, so now it is a standalone computer for $10 more, but still constrained by the limited software of CP/M-68K. The next level up is really beyond my headlights (even CP/M 68K is a stretch for me), i.e., Unix/Linux, but it is something I like to learn. My understanding is 68000 may run uCLinux, but not Linux so onward to 68030 which is surprisingly not very expensive anymore, so yet another $10 to a Linux-ready 68030 which may be more usable. I'm just groping in the dark, who know what sticky mess I may bump into along the way.

I did have a brief flirt with 68060 in the 90's. It was 68060 tightly connected to a FPGA to help me debug hardware and develop software. It never matured past the prototype stage. I don't remember much details after 20+ years. 68060 remains very expensive, I doubt I'll ever work on it again--68040 is plenty good enough.
 
canon-cat-drive.jpg
ClassicHasClass said:
What fix??
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Hi Bob
There is a small piece of nylon plastic that is under tension and will fail. It causes the guide rail to come off its mount, for the head assembly. This causes the floppy case to catch against the R/W head. The first tendency is to use a little more force to get the disk out of the drive. This rips the head off the head lever. I don't know anyone that can fix this, since this isn't a common drive.
In the picture you can see the head assembly has fallen out. On this one, not my drive, the ceramic head was ripped off. If you look in the upper right quadrant, you can see an arc cut as part of the floppy ejector. Right above this arc, you can see a silver colored, philps screw. Under it is the broken nylon end that held the guide rod in place. There was originally a small tab at the left of the screw to hold the rod in place. This is now gone.
In every drive that I've seen, that hasn't yet failed, I've seen that the tip already has a crack and is about to fail.
There are several solutions. On mine I made a piece to go under the screw that was not nylon and would not fail over time ( I forget what it was ).
Another solution is to use a little JB weld to hold the end of the rod down. The only issue with either of these is to make sure that you don't block the end travel of the head carriage.

On a side note, I have some Forth code that one can enter that will allow you to print to a HP printer with PCL5. Other than Canon printers, the only printer you can use is a FX80 compatible printer, with the selections you have available. The Forth code is saved to the floppy so you only need to entire it once. It will copy to other floppies that you format with a floppy that has the code on it. Of course, you can delete the code and write out to the floppy if you like. I do use one of the Canon printers in the table as it is more difficult to change the count of printers available.
Dwight
 
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