Block
13
Block
14
Block
15
Block
16
Block 17
Block
18
I
nput/
Output Operation
•
After
receiving
the
command code,
the
device control electronics sends
the
standard
device byte to
the
processor. This
standard
device byte is not
stored
in
the
channel
registers
in
scratch-pad memory.
It
is used to
set
the
proper
condition code
as
follows:
Condition Code Definition
3
Device control electronics
is
inoperable.
2 A
termination
interrupt
pending
condition
exists
in
the
device
control electronics on
the
multiplexor
channel.
2
The
device
control
electronics
is
busy
working
with
the
speci-
fied device.
2
The
device
control
electronics
is
busy
working
with
a device
other
than
the
one specified.
1
An
external
device
request
interrupt
pending
condition
exists
in
the
device
control
electronics on
the
multiplexor
channel.
1
The
specified device
is
busy
but
the
device
control
electronics
is
not
busy
(i.e.,
tape
rewinding,
off-line
seek).
*1
The
specified device
is
inoperable.
0
The
specified device
and
control
electronics
is
available.
*
If
the
command
is
a Sense,
the
condition code
is
set
to
0
permitting
the
operation
to
be
initiated.
• A
test
is
made
to
see
if
the
condition code is
set
to 0
(input/output
operation
can
be
initiated).
•
If
the
condition code is zero, a
test
is made to see
if
the
specified chan-
nel is
the
multiplexor channel.
•
If
the
specified channel is a selector channel,
the
Channel
Address
Word
and
Channel Block Address
(if
T =
1)
are
fetched
from
main
memory
locations 72
through
79
and
stored
in
the
appropriate
channel
address
register.
Using
the
main
memory
address
specified
in
the
CAW,
the
Channel Command Word is fetched
from
main
memory
and
stored
in
the
appropriate
channel command registers.
•
The
command is
sent
to
the
specified device control electronics
and
the
Start
Device is
terminated
(with
the
condition code
set
to
0).
The
input/
output
operation is
initiated
and
proceeds
under
control
of
the
appropriate
channel
and
registers
in
scratch-pad memory
and
non-addressable
main
memory
(multiplexor devices).
Normal
program
execution
of
the
next
instruction
continues simultaneously
with
the
input/output
operation.
•
If
the
specified channel is
the
multiplexor channel,
the
command code
in
the
Channel
Command
Word
is
tested
to
see
if a burst
mode
operation
has
been specified.
51
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