IBM System/360 System Programmer's Guide

LOGIC BLOCK EXPI,ANATIONS
1. Your exception routine
instruction issued by
prograIP.
receives
the OPEN
control via an XCTL macro-
or EOV routines of the control
2. Use the GETMAIN macro-instruction. The main storage you obtain
must contain all your work areas, including those used to read in a
label or write a label.
3. Use the store mUltiple instruction (STM).
4. Figure 1 in Section I of this chapter provides the information you
need to establish addressability of the DCB address list and work
and control block area for each DCB defined by the OPEN macro-
instruction.
When you receive control from the EOV routine, general register 2
contains the address of the DCB for the oata set and general
register 4 contains the address of the work and control block area
associated with the DCB.
The IECDSECT macro-instruction shown in
chapter symbolically defines the fields of
block area (see Figqre 2 in Section I).
the
the
Appendix
work and
of this
control
You will also need to address the unit control block (UCB) for the
device on which the tape volume is mounted. The address of the UCB
may be obtained from the DXDEBUCB field of the data extent block
defined by the IECDS£CT macro-instruction. The IEFUCBOB macro-
instruction (see Appendix) defines the fields of the unit control
block.
5. Bit configurations in the byte addressed by JFCBMASK+5 incicate
whether label checks or density checks have occurred, and, in the
case of a label check, the condition that caused the check. At
this point, you test bits 0 and 3. If Eit\er cit is set to 1,
processing is required.
6.
The field JFCBMASK is defined by the IECDSECT macro-instruction.
Bit settings in the byte at JFCBMASK+5 are defined as:
Bits
o
1
2
3
4-7
setting
1
1
1
1
Meaning
Label check has occurred.
Standard label (SL) specified; no label/
nonstandard label on mounted volume.
No label (NL) or nonstandard label (NSL) speci-
fied; standard label on mounted volume.
Density check has occurred.
Reserved for future use.
If your installation supports a protection and
scheme involving nonstandard labels, and/or you
retention date and protection checking on standard
incorporate code in your editor routines to check
and retention date expiration.
retention date
want to maintain
labels, you must
for protEcticn
If checking is desired, you must, at this point, read the first
record and determine the label type.
To perform
t:he I/O
operation, move your
CCWs into the
channel
progran;
field
of the work and control tlock area. The
synibolic
name for the first
entry in this field is DXCCW.
Then
issue
an
EXCP macro-instruction
specifying
trle
address of the
control
Label Processing Routines 61

IBM System/360 Specifications

General

Brand	IBM
Model	System/360
Category	Desktop
Language	English