Channel Command
Word (CCW)
(Coot;'d)
Input/Output
Operation
ferred
indicates unusual conditions
that
occurred
as
a
result
of
the
last
operation performed by
the
device.
(The
information received is defined in
the
individual
input/output
device reference manuals.) The address speci-
fied by
the
CCW is
the
leftmost main memory location
of
the
input
area.
Note:
Parity
is not checked on
data
transferred
to main memory by this
command.
Read Reverse
(0010)
- Information is
transferred
from
the
specified
input/output
device to
main
memory in descending order. The address
specified by
the
CCW is
the
rightmost
main
memory location
of
the
input
area.
Write
(0011)
- Information is
transferred
from
main
memory to
the
specified
input/output
device.
The
address specified
by
the
CCW is
the
leftmost main memory location
of
the
output
area.
Write Erase
(0100)
- Information is
transferred
from
main
memory
to
the
specified
input/output
device control electronics.
Data
is
not
written
to
tape
and
the
tape
is erased in accordance
with
the
byte count (applicable
to
magnetic tape only). The address specified by
the
CCW is
the
leftmost
main memory location of
the
output area.
Read
(0101)
- Information is
transferred
from
the
specified
input/
output
device
to
main memory in ascending order. The address specified by
the
CCW is
the
leftmost main memory location of
the
input
area.
Write Control
(0111)
- Information is
transferred
from
main
mem-
ory
to
the
specified
input/output
device control electronics. The device
control electronics
interprets
this information
as
control information
and
initiates a function
not
involving a
data
transfer.
The
address specified by
the
CCW is
the
leftmost main memory location of
the
output
area.
Transfer
in
Channel (10.01) - This command provides chaining
of
CCW's
that
are
not
located in adjacent double word
main
memory. An
actual branch
to
the
address of
the
next
CCW is taken. The
branch
address
(specified in bits 8
t~rough
31
of
the
channel command word)
must
specify
a double word location. (Bits 29
through
31
must
be zero.) This command
cannot be the first command
in
a chain. A
Transfer
in Channel command
may
address
another
Transfer
in Channel command.
Note:
The
flag bits
are
ignored
if
a
Transfer
in Channel command is
specified. The flag bits of
the
preceding command remain effective.
Bit
Positions 8 through 31 (see CCW
format)
contain
the
address
of
the
first byte in main memory
at
which
the
input/output
operation begins,
or
if
the command is a
transfer
in channel,
the
main memory
address
of
the
next CCW to be executed. The address
of
the
first byte
of
the
next
data
segment can also be specified
if
data
chaining.
Bit
Positions
32
through
36
are
the
flag bits
and
have
the
following
significance:
1.
Bit
position 32 is
the
Chain
Data
flag
(CD).
In
addition
to
trans-
ferring
data
to
and
from
a single main memory area,
the
70/46
Processor can read into,
or
write
from,
many
non-contiguous
areas
of
main memory by executing one
Start
Device instruction. When
data
chaining is specified by
setting
this
bit, a chain (series
of
channel command words in sequence) is used
and
each channel com-
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