Description for CS/A SCSI, version 1.0
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whatsit : SCSI interface for CS/A bus
I/O     : ports at $870-$e87f
Mem     : --

IC1 selects the I/O range $87*, and IC2 selects the right registers.
IC6, 7 and 10 make up the SCSI data port at $870. IC11 and 12 compute the
parity. IC8 reads the status lines of the SCSI bus.
IC5 outputs SCSI control lines. The two parts of IC13 controlled
by IC5 are used as pseudo Open Collector for arbitration purposes.
The lower half of IC9 implements a hardware handshake to simplify
data transfer: a simple read or write acknowledges a /REQ request
from the bus.

During arbitration the data bus outputs are decoupled from the
data bus (D1 through IC5) and  also lowers data bus 7 to indicate
SCSI ID 7 (highest priority - the ID is hardcoded). 

For operation with another controller this controller must not drive
the SCSI data bus. But this is not implemented. So only one controller
is possible.

Also I/O can not be driven by the controller so deselect/reselect
can not be supported.

The SCSI protocol can be seen from the SCSI(-II) standard.

The usual rules for SCSI cable termination etc. apply.

See also several SCSI FAQs on the internet.