68k homebuilts

[Dave McGuire]

On Dec 12, 2008, at 6:03 PM, bfranchuk at jetnet.ab.ca wrote:
>> A simple design with a real 68K processor isn't that hard to whip up
>> or debug - in fact not much harder than a simple 6502 or Z80 system.
>> SRAM, of course, is simpler to implement than DRAM, but DRAM can be
>> easier to expand over a couple of MB (for 1MB or less, I'd stuff in a
>> couple of JEDEC RAM sockets for a 16-bit RAM field).  Let me amend
>> "simple" - simple is peripheral chips and memory that can keep up  
>> with
>> the cycle time of your processor so that you don't have to handle
>> wait-states, etc., and can therefore tie DTACK to ground (as  
>> advocated
>> by a famous newsletter, "DTACK Grounded".  At 4MHz to 8Mhz, it
>> shouldn't be a problem these days unless you have a particular VLSI
>> chip you want to use for I/O (6821, 6522, etc.) and it isn't fast
>> enough.  ROM and RAM that are fast enough shouldn't be an issue, even
>> with inexpensive parts.
>>
>>
> Was not that newsletter for a APPLE II, co-processor board?
> Did anybody ever use one, or any kind of general purpose co-processor
> boards for the PC?

   I used to use a CP/M board in my XT, back when an 8MHz 8088 was a  
"real screamer".  It had 64KB of onboard memory, and I had a little  
program that ran from autoexec.bat on the XT which made my DOS- 
available memory 704KB using that board.  It otherwise sat idle when  
DOS was running.

             -Dave

-- 
Dave McGuire
Port Charlotte, FL