TRS-80 Question

[Eric Dittman]

On 4/11/22 11:56 AM, Bill Gunshannon via cctalk wrote:
> 
> Here's one for whatever TRS-80 gurus still hang out.
> 
> The Mode 4 had 64K RAM and pretended to be a Model III by loading
> an image of the Model III Rom and then running it.  Would it be at
> all possible to do the same thing with an image from the Model I
> and thus make a Model 4 capable of running Model I programs?

The Model 4 had the Model III ROM included.  It was the Model 4P
that had to load the Model III ROM image from disk before operating
in Model III mode.

There were some hardware differences between the Model I and Model
III, such as the disk interface being memory-mapped in the Model I
and port-mapped in the Model III, but if the Model I programs don't
use anything that's different in the Model III then the Model 4 in
Model III mode should be able to run them.  So a game that's loaded
from cassette should work but a game that runs from disk and writes
to the disk won't work.
-- 
Eric Dittman