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IBM System/360 System Programmer's Guide

IBM System/360
137 pages
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Explanations
of
Logic
Blocks
1.
The
entry
is
in
the
form
of
an
XCTL
macro-instruction
issued
by
the
control
program.
2.
Use
the
GETMAIN
macro-instruction
to
obtain
main
storage.
3.
Use
the
store
mUltiple
instruction
(STM).
4.
TO
locate
the
address
of
the
data
control
block
(DCB) ,
use
contents
of
register
5.
To
determine
if
the
DCB
is
open,
test
3
of
the
DCBOFLGS
field
of
the
DCB;
if
this
bit
is
zero,
the
has
not
been
opened.
(The
symbolic
names
of
all
fi¢lds
in
the
are
defined
by
the
DCBD
macro-instruction.)
the
bit
DCB
DCB
5.
To
determine
if
a
tape
data
set
is
being
processed,
test
the
UCB3TAPE
field
of
the
unit
control
block
(UCB);
this
bit
is
one
for
a
tape
data
set.
The
symbolic
names
of
all
fields
in
the
UCB
are
defined
by
the
IEFUCBOB
macro-instruction.
(The
macro-definition
and
how
to
add
it
to
the
macro-library
are
in
the
Appendix
of
this
chapter.)
The
address
of
the
UCB
is
contained
in
the
DXDEBUCB
field
of
the
data
extent
block
(DEB)
as
defined
by
the
IECDSECT
macro-instruction.
(The
macro-definition
and
how
to
add
it
to
the
macro-library
are
in
the
Appendix
of
this
chapter.)
6.
To
determine
if
nonstandard
labels
have
been
specified,
test
the
JFCBLTYP
field
of
the
job
file
control
block
(JFCB);
this
field
contains
a
hexadecimal
04
when
nonstandard
labels
have
been
specified.
7.
The
final
DCB
entry
in
the
list
of
DCB
addresses
contains
a
one
in
its
high-order
bit
position.
8.
Add
4
to
the
contents
of
register
5;
add
8
to
the
contents
of
register
6.
9.
Set
the
high-order
bit
to
zero
in
the
SRTEDMCT
field
of
the
UCB.
10.
To
determine
the
type
of
I/O
operation
specified
in
the
OPEN
macro-instruction,
check
the
bit
configuration
of
the
high-order
byte
of
the
DCB
entry
in
the
list
of
DCB
addresses.
The
bit
configuration
for
each
type
of
I/O
operation
is
shown
below.
(The
high-order
four
bits
correspond
to
the
disposition
of
the
data
set;
the
low-order
four
bits
correspond
to
the
I/O
operation
itself.
For
example,
the
bit
configuration
xOll0000
indicates
a
data
set
opened
for
input
whose
disposition
is
LEAVE.)
11.
To
the
mode
(The
DCBD
52
Bits
o 1
x 0
x 0
x 0
2 3
o 1
1 1
o 0
4 5
x x
x x
x x
x x x x 0 0
x x x
xli
x x x x 0 0
x x x x 0 1
x x x x
0 0
x x x x 0 1
6 7
x x
x x
x x
o 0
1 1
1 1
1 1
o 1
o 0
REREAD
LEAVE
Neither
REREAD
nor
LEAVE
INPUT
OUTPUT
INOUT
OUTIN
RDBACK
UPDAT
determine
the
mode
of
the
data
set,
test
the
high-order
bit
of
DCBOFLGS
field
of
the
DCB.
If
this
bit
is
one,
the
data-set
is
output;
if
this
bit
is
zero,
the
data-set
mode
is
input.
symbolic
names
of
all
fields
in
the
DCB
are
defined
by
the
macro-instruction.)

Table of Contents

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IBM System/360 Specifications

General IconGeneral
BrandIBM
ModelSystem/360
CategoryDesktop
LanguageEnglish

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