Re: Is it possible to ADD ROM to a IIe?

[dempson@actrix.gen.nz (David Empson)]

Jeff Blakeney <CUTjefbla@bconnex.net> wrote:

> If you boot the DOS 3.3 System Master disk (it came with my IIe when I
> bought it in 1983) Integer BASIC and Applesoft BASIC are both placed
> in memory.  The former from disk, the latter from ROM.  You could
> switch between them using the commands INT for Integer BASIC and FP
> for Applesoft.  This only works in DOS 3.3, it won't work in ProDOS.
> Although, I suppose someone could write INTEGER.SYSTEM to use in place
> of BASIC.SYSTEM or something.

Yes, that would be possible, but it would have even less memory
available than under Applesoft, since you would need the code from
Integer BASIC itself along with most of the code in BASIC.SYSTEM.

> The section of memory that holds the BASICs is switchable between two
> different memory banks.

Well, _at least_ two banks.  In a 128K IIe, it has a total of five banks
in the $D000-$DFFF area.  The 128K IIc has six banks in this area.

The $E000-$FFFF has three banks (four in the IIc).

In a 64K IIe, or a II+ with a language card installed in slot 0, there
are three banks in $D000-$DFFF, two in $E000-$FFFF.

> One holds Integer, the other Applesoft.

Under DOS 3.3, yes.  (Usually, and assuming INTBASIC was loaded.)

> I don't think this memory bank is big enough to hold BASIC.SYSTEM

Nope.  The "language card" area in question is used to hold the ProDOS
operating system.  BASIC.SYSTEM lives at the top of the main 48K memory
area, roughly in the same memory area as DOS 3.3 normally lives.

> so I still don't think it you can do the switchable in memory thing under
> ProDOS.

Definitely not.

> I've never heard of adding Integer BASIC to the ROMs of a IIe.

You couldn't do it in the motherboard ROMs unless you want to create a
machine that is not compatible with most IIe software.  It is possible
in theory, but you would have to lose Applesoft in the process.

You can do it with an Integer BASIC ROM card, but it won't work in
ProDOS, and can be problematic in DOS 3.3: you need to patch DOS so that
the INT command works correctly - it normally looks for INTBASIC in slot
0, and the Integer BASIC card would have to be in another slot in a IIe.

I believe it is possible to set up a DOS 3.3 based system in which DOS
itself is moved into the language card, Applesoft comes from the
motherboard ROM, and Integer comes from a ROM card.  This frees up most
of the memory area normally occupied by DOS.

I haven't done this myself, so I can't be certain, but it seems
feasible.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand