a classiccmp electronics project?

From: Bill Sudbrink <wh.sudbrink_at_verizon.net>
Date: Sun Aug 1 20:56:29 2004

> A cute trick commonly used in the CP/M days (and later) was to put a
> boot EPROM board in the same (conflicting) memory space with RAM; the
> EPROM code would proceed to "block copy" itself in place (read: EPROM;
> write: RAM) then reset a flipflop that enabled the EPROM board.
>
> EPROM board read access generated many wait states; the trick was the
> EPROM board ignored write cycles but the underlying RAM didn't. I forget
> how we handled the EPROM 'read' cycle but it was buss-safe (S100) and
> simple.

I believe that was the "PHANTOM" line... pin 67 (according to _THE_S-100_
AND_OTHER_MICRO_BUSES_ by Poe and Goodwin).
Received on Sun Aug 01 2004 - 20:56:29 BST