Re: Apple //e With 6502AP

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

Bryan Parkoff <BParkoff@satx.rr.com> wrote:

>     I have noticed that it is an unenhanced Apple //e that has 6502AP with
> 2MHz instead of 65C02.

Sounds perfectly normal to me.  An unenhanced IIe is supposed to have a
6502 processor.  The 2 MHz CPU was used in the IIe because of timing
issues.

> It does have 80 column and double high resolution.

Both of these features are available on an unenhanced IIe.

There is only one exception: the original revision of the US model IIe
(revision A) doesn't support double hi-res graphics.  This capability
was added in revision B, but that was still a long time before the
enhanced IIe came out.

> How is it possible because it is only 6502?

The IIe will operate with either a 6502 or 65C02 (whether it has
original or enhanced firmware).

> There is no way to use Main and Aux 64K memory location. 

Yes there is.  That is a hardware feature of the motherboard.  It has
nothing to do with the firmware version or the type of CPU installed.

> It appears to show "Apple ][" during cold reboot.

An unenhanced Apple II is supposed to display "Apple ][" on startup, so
everything sounds normal.

The Apple ][+ would show "APPLE ][" (note the capitals instead of mixed
case: the Apple ][+ didn't have lower case as a standard feature).

An enhanced Apple IIe would should "Apple //e" (using slashes instead of
square brackets, and adding the 'e').

The enhancement kit for the IIe consists of four chips:

- A 65C02 processor, which replaces the 6502.
- New versions of the CD and EF firmware ROMs, which fix bugs and add
some new features.
- A new video ROM, which replaces one of the sets of inverse uppercase
letters with mousetext characters when using the alternate character
set.

In principle, you can replace any one of these three components
independently of the others.  (The CD and EF ROMs must be replaced as a
pair.)

The enhanced IIe firmware does not contain any 65C02 instructions, so it
will work with either a 6502 or 65C02.  Software is completely unaware
of what is inside the video ROM, so you can use the original or enhanced
one and only the user would be able to tell the difference because of
what was displayed on the screen.

In practice, it is a bad idea to install the enhanced IIe firwmare
without also upgrading the CPU to a 65C02, because most applications
check the firmware version to identify whether a 65C02 is present.  If
you installed the enhanced firmware in a IIe but left the 6502
processor, some applications would try to use 65C02 instructions and
would probably crash.  A well behaved application which requires a 65C02
should be checking the CPU directly rather than relying on the firwmare
version.

The other way around (65C02 processor in combination with original IIe
firmware) is less likely to cause problems.

-- 
David Empson
dempson@actrix.gen.nz