[Coco] External CHAR ROM for 6847

[RETRO Innovations]

On 11/21/2024 3:39 AM, Phill Harvey-Smith via Coco wrote:
> On 21/11/2024 04:38, Bruce Borer via Coco wrote:
>> 2.) Replace the ROM with a larger Flash chip and program it with
>> several images that you can select. This is simpler
>> but does not allow changing the image in-circuit but would allow
>> several images to select.  The selection could be done
>> by switches or a latch that can be selected with firmware.
>
> This is essentially what the Dragon 200e did (except with a single
> font), to allow Spanish characters on that machine.
>
> John Whitworth extended this with a dip switch and multiple fonts :
>
> https://dragonpluselectronics.com/dragon-200e-lower-case-daughterboard/
>
> Cheers.
>
> Phill.
>
As did Ed Snider's (I believe his came out first, but not sure how many
he produced):

https://thezippsterzone.com/2018/05/09/mc6847-external-character-rom-1/

And, my test PCBs for lowerkit and the Dragon 200e lowercase mode also
include a switch for multiple fonts.

But, to Bruce's point, the idea would be to "change" the font under SW
control, not DIP switches, which is tough on the VDG, as there's little
way to address the IC (your only way to interact with the VDG is the 6
IO bits on the PIA that are connected to inputs of the VDG, and those
are needed for setting video modes. You could potentially use them
during the retrace period, like CoCOVDG does, but it's not trivial.

Jim

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