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IBM System/360 System Programmer's Guide

IBM System/360
137 pages
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Bytes
10,
11,
and
12
indicate
the
address
of
the
data
extent
block.
The
request
element
is
normally
12
bytes
in
length;
however,
in
a
multitasking
environment,
it
includes
4
wore
bytes
that
indicate
the
address
of
the
TCB.
•
Register
2
contains
the
address
of
the
input/output
block
(lOB).
•
Register
3
contains
the
address
of
the
data
extent
block
(DEB).
•
Register
4
contains
the
address
of
the
data
control
block
(DCB).
•
Register
7
contains
the
address
of
the
unit
control
block
(UCB).
The
system
places,
into
register
14,
the
address
of
the
location
in
the
input/output
supervisor
to
which
control
is
to
be
returned
after
execution
of
the
appendage.
When
passing
control
from
an
appendage
to
the
system,
you
may
use
displacements
to
the
return
address
in
register
14
for
optional
return
procedures.
Some
of
these
procedures
differ
in
their
treatment
of
the
request
element
associated
with
the
channel
prograrr.
You may
not
change
register
1
in
an
appendage.
Register
9,
if
used,
must
be
set
to
binary
zero
before
control
is
returned
to
the
system.
All
other
registers,
except
those
indicated
in
the
descriptions
of
each
appendage,
must
be
saved
and
restored
if
they
are
used.
The
types
of
appendages
are
listed
in
the
following
paragraphs,
with
explanations
of
when
they
are
entered,
how
they
return
control
to
the
system,
and
which
registers
they
may
use
without
saving
and
restoring.
start
Input/Output
(SIO)
Appendage
This
appendage
is
entered
before
the
input/output
supervisor
issues
a
start
input/output
(SIO)
instruction
for
an
I/O
operation.
If
the
return
address
in
register
14
is
used
to
return
control
to
the
input/output
supervisor,
the
I/O
operation
is
executed
normally.
You
may
optionally
bypass
the
SIO
instruction
and
prevent
execution
of
the
channel
progra~
by
using
the
contents
of
register
14
plus
4
as
the
return
address.
In
this
case,
the
thannel
program
is
not
posted
complete,
but
its
request
element
is
made
available.
You may
use
registers
10
and
11
in
a
start
input/output
appendage
without
saving
and
restoring
their
contents.
Program
Controlled
Interruption
(PCI)
AEEendage
This
appendage
is
entered
when
a
program
controlled
interruption
occurs.
At
the
time
of
the
interruption,
the
contents
of
the
channel
status
word
will
not
have
been
placed
in
the
"channel
status
word"
field
of
the
input/output
block.
The
channel
status
word
can
be
obtained
from
location
64.
You
must
use
the
return
address
in
register
14
to
allow
the
system
to
proceed
with
normal
interruption
processing.
You may
use
registers
10
through
13
in
a
program
controlled
interruption
appendage
without
saving
and
restoring
their
contents.
End-of-Extent
Appendage
This
appendage
is
entered
when
the
seek
address
specified
in
the
input/output
block
is
outside
the
allocated
extent
limits
indicated
in
the
data
extent
block.
82

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IBM System/360 Specifications

General IconGeneral
BrandIBM
ModelSystem/360
CategoryDesktop
LanguageEnglish

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