Specifications

The
DSSI
bus
has
the
following characteristics:
4 Mbytes-per-second
bandwidth
Single-ended
bus
transfers
Up
to
eight
nodes (up to two
host
adapters
and
six
mass
storage devices)
Eight
data
lines
One
parity
line
Eight
control lines
DSSI architecture
features
a DSSI
host
adapter
and
DSSI
mass
storage
devices. The
DSSI host adapter, located on
the
KA640 CPU module, is
the
interface between
the
DSSI
mass
storage devices
and
the
CPU.
The
DSSI
mass
storage devices, such
as
the
RF30, contain a built-in controller.
DSSI architecture improves
system
performance
through
the
following:
DSSI
bus
handles
all
mass
storage
transactions
(Q-bus is free for
other
activity).
DSSI
bus
is
faster
than
the
Q-bus.
Mass
storage devices
can
act
independently
(since each device
has
its
own controller, several devices
can
work simultaneously).
The
DSSI
bus
supports
up
to
eight
daisy-chained nodes. These eight nodes
might
be one DSSI host
adapter
and
seven DSSI
mass
storage devices, such
as
seven RF-series disk drives.
Atypically, a
DSSI
mass
storage device
can
maintain
connections to more
than
one DSSI adapter. Since
the
DSSI
adapter
is located on
the
KA640
CPU
module, a DSSI
mass
storage device
can
connect to more
than
one
KA640
CPU
module.
For
example,
an
external
DSSI cable
can
connect two MicroVAX 3400
systems. The DSSI bus,
in
this
case, would consist of two DSSI
host
adapters
and
up
to six RF30
disk
drives.
The
two MicroVAX 3400
systems
would
have
access to each drive
on
the
DSSI bus.
For
more information
about
connecting two Micro
VAX
3400 systems
and
the
advantages
of
this
configuration,
refer
to
the
section Dual-Host Capability,
found
in
the
Operation manuaL
1-2
MicroVAX 3400 VAXserver 3400 Technical Information