S-100 phantom (Was: RE: Northstar Horizon)

From: Bill Sudbrink <bill_at_chipware.com>
Date: Tue Nov 2 14:43:22 1999

> Ah, ever hear of phantom... part of the MDS-A and VDM IO hack was to set
> them up to output Phantom, in both cases it was just a jumper required.
> The disable was simpler, MDS-A has a rarely used sector interupt enable
> latch and the VDM used a bunch of bits for windowshading, something I
> considered useless and removed from the board (a few socket level jumpers)
> and I had the bit I needed for enable. If they were enabled phantom was
> generated, if they were not ram was there.

I'm getting to this point with my IMSAI restoration. The
ROM on the Cromemco 4FDC can be disabled via an I/O
write... the SDS Expandoram will enable/disable based on
phantom (line 67). Unfortunatly, this seems to control the
whole board. How was phantom used historically? Are there
common boards which generate phantom as factory built? I'm
now using a Cromemco ZPU which seems to work fine, but I have
no docs for it. Does it have a "phantom latch"?

Thanks,
Bill Sudbrink
Received on Tue Nov 02 1999 - 14:43:22 GMT