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

[Darren A]

On Sun, Mar 15, 2015 at 5:12 AM, Gene Heskett <gheskett at wdtv.com> wrote:

>
>
> The delays in the additional decoding will allow some narrow noise to get
> to the /CS lines on the OEM PIA's.  Because of that, we'd have to get
> our address from a point in parallel with the on board 138's inputs.
> And with more modern, read faster cmos versions that would give us the
> 138's function, we might be able to get /SLENB enough nanoseconds ahead
> that the noise would not activate the on board PIA's at all.
>


The address bus and R/W are stable long before the rising edge of E.
Devices do not drive the data bus until E is high, so there is plenty of
time for the additional decoding to assert SLENB before an internal PIA or
ROM activates its data outputs.

I have successfully used SLENB! to replace the Reset and Interrupt vectors
with ones residing on a cartridge ROM.  It works fine.

- Darren