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Note:
When
CLOSE
is
issued
for data sets on magnetic tape volumes,
labels are processed according to bit settings in the OFLGS field of the
data control block.
Before issuing CLOSE for magnetic
tape,
you
must
set the appropriate bits in OFLGS.
The OFLGS bit positions that you are
concerned
with
are
listed
in
the
description
of
the
EOV
macro-
instruction.
CONTROL BLOCK FIELDS
The fields of the input/output
extent
block are illustrated and
fields have been
described
with
block, event control block,
and
data
explained here; the data control block
the
parameters
of
the
DCB
macro-
instruction
instruction
in
the
section
"EXCP
Programming
Specifications."
Input/Output Block Fields
The input/output block is not automatically constructed by
a
macro-
instruction;
it must be defined as a series of constants and must be on
a full-word boundary.
For nondirect-access
devices,
the
input/output
block
is
32
bytes in length.
For direct-access devices, 8 additional
bytes must be provided.
In Figure 10, the shaded areas indicate
fields
in
which
you
must
specify
information.
The other fields are used by the system and must
be defined as all zeros.
You
may
not
place
information
into
these
fields, but you may examine them.
lOB
Address
+4
+8
+12
+16
+20
+24
+28
+32
+36
All
Devices
Direct-
Access
Devices
Only
Figure 10.
Input/Output Block Format
Flags 1 (1 byte)
specifies
the type of channel program.
You must set bit positions
0, 1, and 6.
One bits in positions 0 and 1 indicate data
chaining
and
command
chaining,
respectively.
(If both data chaining and
command chaining are specified,
the
system
does
not
use
error
recovery
routines
except
for the 2311, 2671, 1052, and 2150.)
A
one bit in position 6 indicates that the
channel
program
is
not
related
to
any
other channel prograrr.
Bit positions 2, 3, 4, 5,
and 7 are used only by the system.
Execute Channel Program (EXCP) Macro-Instruction
93
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