[Coco] MC10 guys feeling left out of the DIY discussion?

[Darren A]

On Thu, Mar 12, 2015 at 11:53 AM, Juan Castro wrote:

>
> On Thu, Mar 12, 2015 at 1:23 PM, Darren A wrote:
>  > I spent most of last weekend just trying to figure out how to get the
> HC11 to share RAM with the 6847 VDG without producing any sparkles (no SAM
> chip in this computer).
>
> Dual-port SRAM?
>


It uses standard SRAM and requires two separate 3.59 Mhz clocks (one for
the MCU and one for the VDG) both derived from the same 14.318 Mhz crystal.
Then it is a matter of strecthing the VDG clock cycles until the leading
edge of the HSync pulse falls in the center of the high portion of the
MCU's E cycle.


> Next up will be to devise a PS2 keyboard interface which can mimic the
> MC-10 hardware.
>
> Maybe you can reverse-engineer Cloud-9's one?
>


No need to reverse-engineer, but I'm pretty sure my design will be very
similar.  A cross-point switch in a CPLD along with a ATtiny micro
controller seems to be a fairly common approach for retro projects.

- Darren