Re: RAM cards for IIe

[David Wilson <david@uow.edu.au>]

"Paul R. Santa-Maria" <paulrsm@buckeye-express.com> writes:
>Okay, Bill, now that you have the 4MB IIgs
>RAM card done, how about a Slinky clone
>that holds 64MB (four 16MB SIMMs)?

>I think the Slinky uses three bytes for
>addressing, so 16MB (four 4MB SIMMs or
>one 16MB SIMM) might be the limit for
>compatibility.

>Even 4MB (four 1MB SIMMs) would
>still be nice in an Apple IIe.

There is no reason to make it strictly Slinky compatible
as Apple always recommended that you access it through the
Smartport firmware. That said, the card would be much more
expensive to manufacture than the IIgs card.

1) Needs 8 bit bi-directional buffer on data bus to handle load
of 6 other cards on the slot data bus. Minor cost.
2) Needs a 4KB EPROM and decoding logic to hold Smartport/ProDOS block
driver code. Significant cost.
3) Needs logic to refresh all the RAM. This is the killer. The IIgs memory
slot is designed to have DRAM plugged into it so arranges to refresh it. 
The Apple II bus does not (hence the ribbon cable to the motherboard on
the original 16KB language card). Major cost.

The 8-bit Smartport allows 2**24 blocks of 512 bytes using READBLOCK and
WRITEBLOCK (8GB !!!) while the READ/WRITE commands only allow access to
2**24 bytes limiting it to 16MB which would work with a slinky compatible
design.
-- 
David Wilson  School of IT & CS, Uni of Wollongong, Australia