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generated.
Its
size
ranges
from
4
to
20
bytes, depending on
specifications in the DEVD parameter of this category.
However,
if
you
do not specify the DEVD parameter (and the foundation extension
and common interface portion is generated), the maximum 20 bytes for
this portion are generated.
Some of the procedures performed by the system when the data
control
block
is
opened and closed (such as writing file marks for output data
sets on direct-access volumes) require information
from
optional
data
control
block fields.
You should rrake sure that the data control block
is large enough t:o provide all information necessary for the
procedures
you want the system to handle.
Figure
9
shows
the
relative position of each portion of an opened
data control block.
The fields corresponding to each parameter
of
the
DCB macro-instruction are also designated, with the exception of DDNAME,
which is not included in a data control block that has been opened.
The
fields
identified
in
parentheses represent system inforrr.ation that is
not associated with parameters of the DCB macro-instruction.
Sources of information for data control block fields other
than
the
DCB
macro-instruction
are
data
definition
(DD) statements, data set
labels, and data control block modification routines.
You may
use
any
of
these
sources
to specify DCB parameters.
However, if a portion of
the data control block is not generated by
the
DCB
macro-instruction,
the
system
does
not accept information intended for that portion from
any alternative source.
FOUNDATION BLOCK PARAMETERS:
DDNAME=symbol
specifies the name of
the
data
definition
(DD)
statement
that
describes the data set to be processed.
MACRF=(E)
specifies
that
the
EXCP
macro-instruction
is
to
be
used
in
processing the data set.
EXCP INTERFACE PARAMETERS:
EOEA=symbol
specifies the 2-byte identification of an
end-of-extent
appendage
that you have entered into the SVC library.
PCIA=symbol
specifies
the
2-byte
identification
of
a
program
controlled
interruption
(PCI)
appendage
that
you have entered into the SVC
library.
SIOA=symbol
specifies the 2-byte identification of a start I/O (SIO)
appendage
that you have entered into the SVC library.
CENDA=symbol
specifies the 2-byte identification of a channel end appendage that
you have entered into the SVC library.
XENDA=symbol
specifies
the
2-byte
identification of an abnormal end appendage
that you have entered into the SVC library.
Note:
The full name of an appendage is eight bytes in length,
but
the
first
six
bytes
are
required
by
IBM standards to be the characters
IGG019.
You provide the last two characters
as
the
2-byte
identifi-
cation; they may range in collating sequence from WA to Z9.
Execute Channel Program (EXCP) Macro-Instruction
85
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