MC6847 External Character ROM

I am building a remake of the "Lowerkit" for the CoCo 2.

This external character set board for the 6847 will allow for fonts other
than the built in set in the VDU to be used.  A character set for the 6847
is 2048 bytes (2k), representing 128 ASCII character codes (0 - 127).

This version uses a 16k rom chip, providing room for 8 character sets
selectable in banks by dip switch.

I've put together my first prototype board, and after a little debugging,
it seems to be working great.

MC6847 external character ROM prototype, top and bottom

Prototype in place and working

Here are a few screen shots of the board displaying an alternative font,
and compared to the MC6847 built in character set.  The font needs to 
be refined, but works for testing.

Pics of the external character set being displayed

Compared to the built in character set (1)

Compared to the built in character set (2)

The next step will be to explore moving the logic into a cpld in order to get 
the board size down, and then creating final board layouts for the various
CoCo1 and CoCo2 models.

I've put together an excel spreadsheet that aids in the creation of fonts for
the MC6847 that can be found at the end of the page.  It lets me design a
font in a visual manner, and generates the hex code for the rom.