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Re: [N8VEM: 18763] Motorola MC68020 Project Ideas



Sergey,

I've been thinking about a 16-bit 68000 system even before the ECB Mini-68K CPU board was produced.

A couple of conclusions:  It is easier to interface a 68020 or 68030 to the ECB than it is to interface a 68000 or 68010.  The last two do not drive A0 -- so byte operations become complicated.  The dynamic bus sizing on the 68020/030 are very convenient.

Memory probably needs to be on a separate card.  The 4MEM board has a 16Mhz limit with both the SBC-188 and Z180 Mark IV.  This may be due to the MMU on-board that card, but any discrete MMU will slow things down a little.  The integrated MMU on the 68030 becomes attractive.

My own interest is really "retro," so I still like the idea of a 68000 or 68010; however, the MMU will probably have to be on the CPU card itself.  So this tends to dictate a double-width Eurocard, like that one used on the new 6x0x board, a board with an MMU.  (VME is also double-width Eurocard, but uses 2 connectors, rather than the ECB single connector.)

My own choice would be to stick with ECB, and to be compatible with existing peripheral cards.

--John







On 10/03/2014 11:54 AM, Sergey wrote:
Hi,

The short summer in the Pacific Northwest is coming to its end, and I started to think about projects for the long winter.

I visited a local surplus store yesterday and picked a few MC68020 / 20 MHz processors with sockets... They were real cheap, and I couldn't resist. :-)

So I am thinking about what should I build with these processors. Here are some of my ideas:
- It would be nice to build a computer that could run some kind of UNIX. Unfortunately that means the system will need to have an MMU (and the matching MC68851 PMMU seems to be an unobtainium). Are there any UNIX-like systems that would work without an MMU? Any other OS recommendations? OS-9 could be a good fit, but AFAIK it is not free. Or maybe I should implement some kind of rudimentary MMU (e.g. 74LS612) or use a CPLD?
- It could be a standalone system with processor, memory, several UARTs, block storage (most likely an IDE compatible flash card).
- Or an extendable SBC with VME or ECB bus. VME seems to be a good fit, although I want to keep the board size small, so most likely it will be a single connector 24-bit address/16-bit data VME variety... Here is such a project: http://www.dutch.nl/bdj/vme/68020sys.htm
- Use 32-bit SRAM memory - four 512 KiB chips. Possibly add a connector for a memory card for future extension (and to keep SBC small)

Thanks,
Sergey

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