Re: Language Card

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

Ed Hillman <ehillman@erinet.com> wrote:

> On Fri, 22 Oct 1999 19:42:45 -0400, "Stefan Miganowicz"
> <nrsdpms1@tiac.net> wrote:
> 
> >What exactly does an Apple Language Card do in an Apple II+?
> 
> The "langauage card" was orignally intended to hold in an extra 16K of
> RAM whichever of the two BASIC dialects was not resident in your
> machine's ROM.

Not exactly.  Its actual purpose (and the reason for the name) is that
it was supplied with and required by the "Apple II Language System",
which is better known as Apple II UCSD Pascal.

The ability to have both variants of BASIC available without an
additional ROM card was an added bonus.

Integer or Applesoft BASIC loaded into the language card only uses 12K,
leaving 4K unused.  The full 16K is used with Pascal, and most of it is
also used by the ProDOS kernel.

The card works by switching out the 12K of motherboard ROM, replacing it
with RAM.  This 12K area is divided into two sub-areas: the first 4K
(D000-DFFF) has two separate banks of RAM, and the remaining 8K
(E000-FFFF) is common to both banks.

The language card has soft-switches to independently control read-enable
and write-enable functions for the RAM, and to select the bank.  In
total, there are eight soft-switches:

C080    Read language card bank 1, write protected
C081    Read ROM, write language card bank 1
C082    Read ROM, language card write protected
C083    Read/write language card bank 1
C088    Read language card bank 2, write protected
C089    Read ROM, write language card bank 2
C08A    Read ROM, language card write protected
C08B    Read/write language card bank 2

All of the "write enable" locations (C081, C083, C089 and C08B) require
two accesses to enable writes (subsequent accesses toggle write enable
into the opposite state, I think).  Accessing any of the other soft
switches disables writes.

> Eventually the extra memory on the card was used for other things and
> the cards began to be known as "16K RAM Cards"/

It is also worth noting that the language card functionality is built
into the motherboard on the Apple IIe and later machines (there is no
physical slot 0 any more), and that it is called "bank-switched memory"
in these machines (which is a very silly name, in my opinion, since it
isn't the only type of bank switched memory in the IIe).

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