Re: Platinum IIe ROM chips?

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

Jonathan Adams <az268@chebucto.ns.ca> wrote:

> Could somebody tell me how many ROM chips are in a Platinum IIe and how I
> can identify them?

There are four ROM chips in the platinum IIe, which is the same number
as in other models of the IIe.

Two of them contain the firmware which appears in the $C100-$FFFF memory
region.  They are labelled "CD ROM" and "EF ROM" on the logic board (or
something similar).

The other two are the "Video ROM" (which contains the data patterns used
to display text characters and all graphics modes) and the "Keyboard
ROM" (which contains data patterns used to decode the keyboard and map
row, column and modifier key combinations into the ASCII character set).

All four ROMs are identical to the corresponding ROMs in the enhanced
firmware in the same language variants of the original IIe (either as
shipped by Apple or after installation by the end user from the
enhancement kit, which replaced all but the keyboard ROM).

The CD and EF ROMs are the same in every language variant of the same
model of the IIe.

The video and keyboard ROMs differ between language variants of the IIe.
The US model of the IIe has the simplest versions, consisting of
standard English ASCII characters in text mode in the video ROM, for
example.

International models of the IIe contain two mappings in their video and
keyboard ROMs (which use ROM chips with twice the capacity of the US
model).  A switch on the underside of the keyboard is used to select
which mapping is active.  One setting gives you the US standard display
(English text) and keyboard layout.  The other setting gives you several
localised display characters (e.g. the International English IIe has a
UK pound symbol '�' in place of the US pound symbol '#') and may also
change the keyboard layout (such as swapping the 'Z' and 'Y' keys for
the German model, or reversing the shift key state for the numeric keys
in the French model, if I remember right).

If you want to locate the ROM chips in a specific IIe, you can probably
pinpoint them all by looking for 24 pin or 28 pin socketed chips with
part numbers that start with 341- or 342-.  The firmware ROMs are near
the 40-pin CPU (65C02) and MMU chips.  The video ROM is probably near
the 40-pin IOU chip.  The keyboard ROM is next to the 40-pin keyboard
encoder chip (AY-3600), which is near the keyboard connector.

-- 
David Empson
dempson@actrix.gen.nz