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Re: IIc SD/MMC RAM

In <1homysl.1akj9zoco0cx2N%dempson@actrix.gen.nz> David Empson wrote:
> kaos116 <kaos116@comcast.net> wrote:
> 
>> Yes there is a memory expanision header inside. from what I have read 
>> and remember. All of the ][c's had it except the very first revisions. 
>> I think you could get up to 1 meg inside.
> 
> The memory expansion slot was added in the third generation of the IIc,
> but the second generation (with UniDisk 3.5 support) had basically the
> same logic board as the first generation (differed only in default ROM
> size and serial port clocking).
> 
> The expansion slot is functionally equivalent to a RamWorks card in a
> IIe: it has a single byte bank address which allows auxiliary memory 
> to be switched between up to 256 banks of 64KB, so the theoretical 
> limit is 16 MB, but the hardware interface might not provide all of 
> the bits of the higher address bus.

David, I think your books have been stashed away for too long. The 
original third-party memory cards for the IIc used bank switched memory, 
but Apple's memory card had a slinky interface just like the Apple II 
Memory Expansion Card used in the Apple II models with regular Apple Bus 
slots.

I remembered this because a couple of years ago I looked at making a 
static RAM card for the IIc. Static RAM is so cheap now that a 1MB card 
would be just as cheap as a dynamic RAM card, but easier to make and a 
small backup battery would make it non-volatile. Unfortunately the three 
address registers that hold the 20-bit memory card address have to be 
able to be able to be read as well as written by the IIc, and have to 
automatically increment with each read or write to the data register, so 
the amount of TTL logic needed wouldn't be trivial. A simple FPGA would 
take take care of everything but unfortunately I've had zero experience 
using them.

-- 
* Roger Johnstone, Invercargill, New Zealand -> http://roger.geek.nz
* PS/2 Mouse Adapter for vintage Apple II or Mac
* SCART RGB cable for Apple IIGS