[Coco] 6 Chip ^809 Computer -> Kipper SBC

[RETRO Innovations]

On 3/15/2015 1:12 PM, Gene Heskett wrote:
> Thats faster than the HCT's, suggestions?
A CPLD.

>> 74F or ALS or a half dozen other families get you the speed you need,
>> but I really don't think it's an issue.  If you look at the 6821 data
>> sheet, it's output buffers don't come online until quite a ways after
>> the start of the cycle, so the chance two devices will be on the bus
>> is minimal.
> But it does bear checking with a good scope, else you'll have ground
> bounce to beat all.  BTDT.
I was in a hurry when I wrote the response this morning, and I did not 
have time to check the 6809 timing.  But, Darren makes the best point.  
Even at 2 MHz, address is valid vefore Q high, which is 125ns before E 
high.  Thus, you can safely render the internal '138 inactive 100nS 
before E goes high, as long as one does not use E as a enable signal for 
the '138.

As Darren noes, you can bank out the internal ROMs that way, which is neat.

Jim