[Coco] External CHAR ROM for 6847

[RETRO Innovations]

I know back in the day, kits like "lowerkit" were available to allow an
external char ROM.  I'd like to better understand how the circuit works,
but the datasheet is confusing on the 8 bits of address for the ROM that
appear to be coming from the data bus.

Anyone have knowledge of how this works, or a project schematic that
shows it?  Ed made a repro a number of years ago, but no schematic I can
find.  And, I don't see any open source "lowerkit" project to better
understand it.

Jim

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