[Coco] is there any existing 6847 output to RGB ? (for coco2)

[Darren A]

On Sat, Feb 21, 2015 at 7:58 AM, didier derny <didier at aida.org> wrote:

> In fact, Z18/Z19 are also on the NTSC mc10 so they are not involved in the
> 525 -> 625 conversion
> We checked a Alice motherboard, the Z20 (Z18 on the pcb) seems to be a
> custom chip
> From MTE  (Matra Tandy Electronic)  the company building the Alice
>
> So apparently this chips is doing all the conversion...
>


The flip flops labeled Z18 and Z19 in the Alice schematic are not actually
present on the Alice 4K.  In the MC-10 these are used to synchronize the
VDG clock with the E clock from the MCU (a job performed by the SAM in a
CoCo 1 or 2).  This is necessary because the MCU and VDG need to share
access to the RAM (MCU while E is high and VDG while E is low).

The chip labeled Z18 on the Alice motherboard is a custom chip which
incorporates all the functions of Z18, Z19 and Z20 as illustrated in the
schematic. This includes the clock synchronization along with the ability
to pause the VDG clock during blanking so that the additional lines can be
inserted.

- Darren