Re: TI-H: direct bus access
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Re: TI-H: direct bus access
>
> No. The 6800 can directly address 16MB. Over that ammount you need memory
> addressing such as EMS, but not with the 6800. The ROM needs to be edited,
> or an EMS clone since it only supports 256k. If the ROM were edited, the
> processor could handle over 256k. If anyone is interested in the rom
> hacking, I can give you my cracked rom if you don't give it to apple... ;)
>
Yes, the 68K can access 16MB without paging, however the chip in the TI-92 is
NOT a normal 68K like the one in the Macs. It only has 20 address lines that
we know of, the upper four bits create a mask for chip enable lines (one for
RAM, one for internal ROM, one for external ROM, and one for IO ports). Thus
you are limited to RAM addresses $00 0000 - $0F FFFF, and either the internal
or external ROM addresses (whichever one is NOT present), and addresses above
$60 001F. This still leaves plenty of memory in between, but the TI ROM would
not be able to play with the non-consecutive stuff since it's memory movement
algorithms aren't written for broken memory segments.
I'm playing with the idea of a 1 meg expansion. I don't see much need for
anything more on a TI-92 right now. It's not like you're going to use up 1 meg
with the stuff out there now anyway. (and loading 1MB from an I/O line running
at 9600 baud is gonna take awhile)
--Bryan
bcturner@eos.ncsu.edu
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