Re: BASIC for the CBM-II/8088

Re video emulation:

How much of the components of the B motherboard are socketed and how
much is soldered directly to the board? I've seen some pictures and it
seems like only the largest IC's are socketed.

Looking at the schematics, it would be really easy to add support for a
PC8 char rom and reuse the invert signal (MSB of screen ram data) to
support 256 instead of 128 characters.

It would not be that hard to add an additional of 2k ram as attribute
memory, although it would require a bit more effort. U25 74LS139
already decodes $C000-$DFFFF in 2k steps, where $D800-$DFFF isn't
useable as U24 74S138 already decodes that 2k block into 256 byte
blocks. $D000-$D7FF is already used for existing video ram. $C000-$C7FF
and $C800-$CFFF is free and either one of these could be used for
another 2k which could be used as attribute memory.

Of course this would only be visible by the 6509, but it would still
make it far easier, just copy 4k of data each time the screen needs
updating. Not sure if a 4k block copy (fixed addresses both for source
and destination, and requiring ,Y indirect addressing for either source
or destination) would be too slow to just do on each interrupt.


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