I
Ready
-
The
Ready
signal
is
a block ready in response to the
first
resume
of a block.
The
Ready
signal
is
a pulse
50
±
10
nanoseconds
wide
(at
the
50%
voltage
points).
It
is
sent
from
the external device
to the
CRAY-l.
Resume
-
Resume
is
sent
from
the
CRAY-l
to the external device to
initiate
the synchronous data
transfer
and
to time the sending of
data
at
the
CRAY-l.
The
Resume
pulse
is
50"±
3 nanoseconds
wide
(at
the
50%
voltage
points).
Following the
first
resume,
which
awaits a ready response, the signal
is
sent in
one
group of three
resumes
followed
by
as
many
groups of four
resumes
as
required to
complete the block
transfer.
Disconnect - Disconnect
is
a signal sent
from
the external device
to the
CRAY-l
indicating
that
transmission
from
the external device
is
complete.
It
is
sent
with parcel 2 of the
last
data
word
or
at
any
later
time. Disconnect
is
a pulse
50
±
10
nanoseconds
wide
(at
the
50%
voltage
points).
Block
length
restrictions
-
The
input channel
has
no
restrictions
on
block length.
The
mass
storage
controller,
which
is
the only device
connected to
this
type of channel,
has
rigid
restrictions
on
its
block lengths. Input transmissions are limited to 1 or 4 or
512
64-bit
words.
Cabling
restrictions
-
The
synchronous channels use a fixed length
cable providing constant propagation time
for
the
signals.
This
cable delay
is
designed
into
the control
logic;
therefore,
the cable
length
and
propagation speed cannot
be
changed.
The
total
cable
length
between
the
CRAY-l
and
the external device
is
17
feet
(518
cm).
The
cable
run
for
a synchronous channel uses
one
10
foot
(305
cm)
drop cable
at
the
CRAY-l
and
one
7 foot
(213
cm)
length of data cable
at
the external device.
Clock
- A clock signal
is
supplied over a separate cable (one per
DCU
cabinet) to the external device
from
the
CRAY-l.
This clock
signal synchronizes
signals
at
the external device
interface
connector.
Output channels
Table 6-7
illustrates
a general
view
of
an
output signal sequence.
Data Bits
2°
through 2
15
-
Data
Bits
2°,2
1
,
•..
,2
15
are
signals
carrying a
16-bit
parcel of data
from
the
CRAY-l
to the external
device.
They
are sent with the leading
edge
of
the
Ready
pulse
+ 5 nsec.
Data
Bit
signals
remain
unchanged
on
the
lines
until
the next parcel
is
sent.
Parity
Bits 0 through 3 -
Parity
Bits 0, 1, 2,
and
3 are each assigned
to a
4-bit
group of data
bits.
The
parity
bits
are
set
or cleared to
2240004
6-15
E
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