IBM System/360 System Programmer's Guide

Note: When CLOSE is issued for data sets on magnetic tape volumes,
labels are processed according to bit settings in the OFLGS field of the
data control block. Before issuing CLOSE for magnetic tape, you must
set the appropriate bits in OFLGS. The OFLGS bit positions that you are
concerned with are listed in the description of the EOV macro-
instruction.
CONTROL BLOCK FIELDS
The fields of the input/output
extent block are illustrated and
fields have been described with
block, event control block, and data
explained here; the data control block
the parameters of the DCB macro-
instruction instruction in the section "EXCP Programming
Specifications."
Input/Output Block Fields
The input/output block is not automatically constructed by a macro-
instruction; it must be defined as a series of constants and must be on
a full-word boundary. For nondirect-access devices, the input/output
block is 32 bytes in length. For direct-access devices, 8 additional
bytes must be provided.
In Figure 10, the shaded areas indicate fields in which you must
specify information. The other fields are used by the system and must
be defined as all zeros. You may not place information into these
fields, but you may examine them.
lOB
Address
+4
+8
+12
+16
+20
+24
+28
+32
+36
All
Devices
Direct-
Access
Devices
Only
Figure 10. Input/Output Block Format
Flags 1 (1 byte)
specifies the type of channel program. You must set bit positions
0, 1, and 6. One bits in positions 0 and 1 indicate data chaining
and command chaining, respectively. (If both data chaining and
command chaining are specified, the system does not use error
recovery routines except for the 2311, 2671, 1052, and 2150.) A
one bit in position 6 indicates that the channel program is not
related to any other channel prograrr. Bit positions 2, 3, 4, 5,
and 7 are used only by the system.
Execute Channel Program (EXCP) Macro-Instruction 93

IBM System/360 Specifications

General

Brand	IBM
Model	System/360
Category	Desktop
Language	English