e p chandler wrote:
On Oct 19, 3:03 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
rhohler wrote:
The NuMustang discussion got me thinking. What is the rarest Apple II
card today? Of course, prototype cards are limited and rare but what
production card. I would bet on the Transwarp II card or something.
I have some 128K bubble memory cards that emulate a Disk ][ with
somewhat less capacity. They were made by Helix Labs, and were
intended to provide non-volatile storage for Apple II's used in
harsh industrial environments.
I once considered using one of these in a project which buffered data
from a multi-channel analyzer. The problem with the disk 2 is that it
disables interrupts ([perhaps it was DOS 3.3....) The commercial
solution to the problem used a clock card which itself generated
interrupts. My idea was to write the data to bubble memory instead of
to disk.
It is a fundamental requirement of the Disk ][ controller that no
interruptions occur during reading or writing. Both are timing-
critical operations--the 6502 is running as a real-time disk controller.
I'm not sure whether the bubble memory cards have any real-time
requirements or not... It depends on whether or not the supporting
chips control the bubble shifting asynchronously.
As far as rare cards go, I did see a demo at a club meeting of an
modem card that had a number of special abilities (no I don't live in
silicon valley). It was never produced because it had a tone generator
built in which would have turned the Apple into a blue box (yes I know
the guys at MIT did it first!).
Wasn't that card made to Captain Crunch's specifications? ;-)