48000000
4FOOOOOO
Input/Output
Block
(lOB)
Request
elerrent
for
channel
program
has
been
made
availatle
after
it
has
been
purged.
Error
recovery
routines
have
been
entered
because
of
direct-access
error
but
are
unable
to
read
howe
address
or
record
O.
The
input/output
block
is
40
bytes
in
length
and
immediately
follows
the
event
control
block.
The
section
"EXCP
MacrO-Instruction"
of
this
publication
contains
a
diagram
of
the
input/output
block.
The
only
fields
with
which
the
user
of
XDAP
is
concerned
are
the
"First
Two
Sense
Bytes"
and
"Channel
status
Word"
fields.
You may
wish
to
examine
these
fields
when
a
unit
check
condition
or
an
I/O
interruption
occurs.
Direct-Access
Channel
Program
The
direct-access
channel
program
is
24
bytes
in
length
and
irrmedi-
ately
follows
the
input/output
clock.
Depending
on
the
type
of
I/O
operation
specified
in
the
XDAP
macro-instruction,
one
of
four
channel
programs
may
be
generated.
The
three
channel
corrmand
words
for
each
of
the
four
possible
channel
programs
are
shown
in
Figure
13.
r----------------.----------T-----T-------------------------------------,
I
Type
of
I/O
Operation
I
CCW
I Coromand
Code
I
~--------------------------+-----+-------------------------------------~
I
Read
by
Identification
I 1 I
Search
ID
Equal
I
I I 2 I
Transfer
in
Channel
I
I
Verify
by
Identification
1
1 3 I
Read
Key
and
Data
I
~----------------.----------+-----+-------------------------------------~
I
Read
by
Key
I 1 I
Search
Key
Equal
I
I I
2 I
Transfer
in
Channel
I
I
Verify
by
Key1
I 3 I
Read
Data
I
~----------------.----------+-----+-------------------------------------~
II
1 I
Search
ID
Equal
I
I
Write
by
Identification
I 2 I
Transfer
in
Channel
I
I I 3 I
Write
Key
and
Data
I
~--------------------------+-----+-------------------------------------~
I I 1 I
Search
Key
Equal
I
I
write
by
Key I 2 I
Transfer
in
Channel
I
I I 3 I
Write
Data
I
~----------------.----------i-----i-------------------
__________________
~
I
1For
verifying
operations,
the
third
CCW
is
flagged
to
suppress
the
I
I
transfer
of
information
to
main
storage.
I
L
______________________________________________________________________
J
Figure
13.
The
XDAP
Channel
Programs
XDAP
OPTIONS
CONVERSION
OF
RELATIVE
TRACK
ADDRESS
TO
ACTUAL
ADDRESS
To
issue
XD1~P,
you
must
provide
the
actual
device
address
of
the
track
containing
the
block
to
be
processed.
If
you
know
only
the
relative
track
address,
you
can
convert
it
to
the
actual
address
by
using
a
resident
system
routine.
The
entry
point
to
this
conversion
routine
is
labeled
IECPCNVT.
The
address
of
the
entry
point
is
in
the
communication
veGtor
table
(CVT).
The
address
of
the
CVT
is
in
location
16.
(The
CVT
maGro-instruction
defines
the
symtolic
names
of
all
fields
in
the
CVT.
The
macro-definition
and
how
to
add
it
to
the
macro-library
are
in
the
Appendix
of
this
chapter.)
Execute
Direct
Access
Program
(XDAP)
Macro-Instruction
103
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