Re: Hybrid //c RAM card

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

sfahey <sfahey@a2central.com.remove-poo-this> wrote:

> Would it be possible to create a hybrid //c RAM card that was half Ultra RAM
> I (or II) and half slinky/memory expansion? The Ultra cards don't use the
> RAM expansion port so is it possible for them to co-exist?

Sure, it sounds feasible, given a IIc with the memory expansion slot
(the card would also have to plug into the CPU/MMU sockets), and
assuming there is enough space for the extra circuitry and RAM chips.

> I assume they'd be their own seperate circuits.

Yes. You could use some kind of combined logic chip to cut down the chip
count, but it would be implementing two independent circuits.

> If that's possible, then it would be trivial to add a NSC or D-Clock as well.

Physical height is an issue for these cards - they have to fit under the
keyboard. I doubt there would be enough clearance for a standard Dallas
SmartWatch on top of the card.

You could build the equivalent circuit into the board with a static RAM,
battery and the appropriate controller chip. In principle, this could
work anywhere in the address space of the card, but it would be tricky
to implement in the slinky area due to its auto-incrementing address
register. Auxiliary memory would be easier, but that means you have to
do a bank switch to access the clock.

A simpler memory mapped real time clock chip buried in the slinky area
(after a gap above the maximum supported RAM) makes more sense. It would
need a custom clock driver, which you'd need anyway for a NSC/Dallas.

-- 
David Empson
dempson@actrix.gen.nz