Re: MS-DOS 3.30 boot on the CBM-II

Den Sat, 04 Nov 2017 11:38:42 +0100 skrev Michał Pleban
<lists@michau.name>:
> smf wrote:
> 
> > Are you planning on removing the need to boot msdos 1.25 first?
> 
> Yes, that's the plan. However, I need first to figure out how to issue
> the initial "boot system" command from the 6509 to 8088, something I
> haven't tackled yet.

I assume that involves disassembling both the 8088 ROM and the 6509
software. Maybe someone else could step in here if it's just too much
for one person?

(Unfortunitely I don't own any CBM-II so I can only be of theoretical
help :( )

> Also, first I would like to make a ROMmable version that can be placed
> in the EPROM chip on the board, but I am running out of space now (the
> ROM has only little than 3 kB free space).

First: It is so cool that you have come so far with this project!

Re the rom, it seems like the whole upper 64k is decoded to the rom,
and nothing else resides there, so with just an adapter and some extra
wires it should be possible to have up to 64k rom.

Perhaps it would be a good idea to make a simple board with both ROM
and 64k RAM and some way to switch between ROM and RAM when reading
from the upper 64k. PB7 of the PC side CIA seems to be NC according to
the schematics, so that port could be used to switch between RAM and
ROM.

This could work as a developement thing, and when things will be more
or less finalized it could be replaced by a larger ROM. With 64k ROM it
might even be a good idea to have a ROM disk for some of the most used
files, i.e. COMMAND.COM from the DOS version a user prefers to run.

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