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 [ 12 posts ] 
 68008 on breadboard - 3 ICs system 
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Joined: Mon May 04, 2020 3:29 pm
Posts: 7
Hi,
this is my last toy, a 68008 running at 8MHz on a breadboard with 3 ICs (68008 CPU, 128KB SRAM, PIC18F47Q10 MCU).

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The PIC MCU (on the custom red PCB) emulates the ROM/EPROM, the clock generator, and all the I/O ICs (including the interrupt controller) on the CPU bus.

In this video an example of an automated cross-assembler toolchain using sLoad (a custom s-record loader) and Easy68K as assembler.

Currently I'm starting to design the final board (68k-MBC).

The specs are:

* easy to build (no ROM/EPROM, SMD, GAL, CPLD)
* 68008 CPU @8MHz
* 2 main PCB configurations, the tiniest allows to have a complete system with only 3 ICs
* 2 serial ports
* 16 GPIO (optional)
* I2C expansion port
* RS232 driver onboard (optional)
* 128/512/1024KB SRAM
* RTC module (optional)
* SD module for HD emulation (optional)


We'll see...

Regards.
J4F


Mon Oct 12, 2020 11:00 am

Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1632
Very nice! I think it's a particular category, and an interesting category, of modern retro rebuilds where the glue (and maybe more) is implemented in a microcontroller.


Mon Oct 12, 2020 12:35 pm
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Joined: Fri Mar 22, 2019 8:03 am
Posts: 328
Location: Girona-Catalonia
BigEd wrote:
Very nice! I think it's a particular category, and an interesting category, of modern retro rebuilds where the glue (and maybe more) is implemented in a microcontroller.
That's something to be seriously considered even for more discrete based builds, down to TTL chips or transistors, or I think so. I can imagine that for most hobbyists the biggest interest is in the making of the processor itself, so everything needed around it can be possibly implemented in a dedicated microcontroller. This remains me of the "Single Board Relay Computer", http://relaysbc.sourceforge.net which instead of using a ton of relays to do relativelly uninteresting stuff, it just has an PIC microcontroller in it. Even the relay processor RAM is served by the microcontroller (http://relaysbc.sourceforge.net/semi.html).


Mon Oct 12, 2020 2:30 pm

Joined: Mon Oct 07, 2019 2:41 am
Posts: 256
Add 2 SDC (standard) cards, and use them as dual floppies. Or better yet
emulate cassete tape or stringy floppy.(Sinclair QL?)
I was looking
on ebay for some parts, and came across a 8080 machine with front panel
all emulated by a microcontroler.
All I need now is a good terminal with a low cost micro controler.
Ben.
Ps: Wireless world also had a 68008? design, but I don't know what issue.


Sun Oct 18, 2020 8:04 pm

Joined: Tue Dec 18, 2018 11:25 am
Posts: 40
Location: Hampshire, UK.
@Oldben; are these the Wireless World articles you were thinking of?
http://marc.retronik.fr/motorola/68K/68000/AR226_Designing_with_the_68008_Microprocessor_%5BWirelessWorld_1984_8p%5D.pdf


Sun Oct 18, 2020 9:28 pm

Joined: Mon Oct 07, 2019 2:41 am
Posts: 256
Most likely. Looking back, most the projects seem not quite finshed yet. Like Build Bla Bla Z80 cp/m system but no bios listings or PCB layouts. Also wondered why all 6502 designs in the UK?
The 6809 was a better design choice other than saving a few pennies.


Sun Oct 18, 2020 11:47 pm
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Joined: Mon May 04, 2020 3:29 pm
Posts: 7
68k-MBC: Just finished the PCB routing (now some refinements...).

This board will support two main HW configurations: Lite and Full.
With the Lite configuration it needs only 3 ICs for a running 68008 system.

All the I/O, IRQ controller, Eprom and clock generation is done by the PIC MCU directly on the CPU bus.

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Tue Dec 29, 2020 4:12 pm

Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1632
Very tidy - I like it!


Tue Dec 29, 2020 4:58 pm

Joined: Mon Oct 07, 2019 2:41 am
Posts: 256
I still think of a 3 IC system as a 6502 + friends. Nice to see a simple 68000 cpu with I/O handled
by a smart chip. I can't help to compare this system to mainframes of the 1970's, both similar power but sure a big change in size. Ben.


Tue Dec 29, 2020 8:00 pm
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Joined: Mon May 04, 2020 3:29 pm
Posts: 7
oldben wrote:
I still think of a 3 IC system as a 6502 + friends....


I've a lot of W65C816S8P so they are in my (long) TO-DO list... may be one day...


Fri Jan 01, 2021 4:33 pm
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Joined: Mon May 04, 2020 3:29 pm
Posts: 7
68k-MBC starts moving...

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Mon Feb 01, 2021 2:08 pm
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Joined: Mon May 04, 2020 3:29 pm
Posts: 7
The 68k-MBC is OUT!

Here the page with all the details.

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Mon Apr 12, 2021 1:31 pm
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