Date   : Mon, 14 Nov 1988 15:09:25 GMT
From   : wilker@tcgould.tn.cornell.edu (Clarence W. Wilkerson Jr.)
Subject: MEX Overlays and SCSI Implementations

For using the z80 SIO, there are several variants , but
the zerox 820 source code should provide a guid. Variants
include the port addresses, whether the two port addresses
are interleaved or not, and how the data rate is set ( this
is external to the z80sio.

  For the scsi question, there are lots of scsi controller
  boards going on the surplus market for under $100, see
  Computer Surplus Store ads in BYTE or Computer Shopper.
  Surplus 10 megs drives are about $100. The port to talk
  to the SCSI drive is basically a bidirectional parallel
  port with several status lines. It is balanced by a
  resistor network to about 3 volts.
    The pc board approach is used by some tandy coco suppliers,
    and I know of at least one such arrangement for Heath Zenith
    H89's. The address lines for memory don't have to be selected,
    you can just address it via ports, but of course you have
    to write the software. The SASI or SCSI software is probably
    more generic.