Table of Contents
Advertisement
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
~----------------.----------+-----+-------------------------------------~
I
I
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
Advertisement
Table of Contents
