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dcb-addr
R - Read a block.
W - Write a block.
V - Verify contents of a block but do
I - Locate a block by identification.
present,
and
the
data
portion
written. )
K - Locate a block by key.
(Only
the
block is read or written.)
not transfer data.
(The
key
portion,
if
of the block are read or
data
portion
of
the
specifies the address of the data control tlock of the data set.
area-addr
specifies the address of an input or output area for a block of the
data set.
length-value
specifies
the
number
of
bytes
to be transferred to or from the
input or output area.
If blocks are to
be
located
by
identifi-
cation
and
the data set contains keys, the value must include the
length of the key.
The maximum
number
of
bytes
transferred
is
32767.
key-ador
specifies,
when
blocks are to be located by key, the address of a
main storage field that contains the key of a block to be
read
or
overwritten.
keylength-value
specifies,
when blocks are to be located by key, the length of the
key.
The maximum length is 255 tytes.
blkref-addr
specifies the address of a main storage field containing the actual
device addrless of the track containing the
1::lock
to
be
located.
When
blocks are to be located by key, this field is seven bytes in
length; when blocks are to be located by identification, an
eighth
byte
indicating
block
identification
must
be
included in this
field.
(The actual address of a block is
in
the
form
MBBCCHHR,
where
M indicates
which extent entry in the data extent block is
associated with the direct-access program;
BB
indicates
the
bin
number
of direct-access volurre; CC indicates the cylinder address;
HH indicates the actual track address; and R
indicates
the
block
identification.)
EOV
End of Volume
The
EOV
mac:ro-instruction
identifies end-of-volume and end-of-data
set conditions.
For an end-of-volume condition, EOV causes switching of
volumes and
verification
or
creation
of
standard
labels.
For
an
end-of-data set condition, EOV causes your end-of-data set routine to be
entered.
When
using XDAP, you issue EOV if switching of direct-access
volumes is necessary, or if secondary allocation is to be performed
for
a direct-access data set opened for output.
The only parameter of the EOV macro-instruction is the address of the
data control block of the data set.
CLOSE -- Restore Data Control Block
The
CLOSE macro-instruction restores one or more data control blocks
so that processing of their associated data sets can be terminated.
You
must issue CLOSE for all data sets that were used by the
direct
access
channel
program.
Some
of
the
procedures
performed
when
CLOSE is
executed are:
Execute Direct Access Program (XDAP) Macro-Instruction
101
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