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In MVS, to make a request for feedback, insert the letter F in the type code of a
READ/WRITE macro (DIF, DAF and so on). The format of the blockaddress field
after feedback, however, is determined by the OPTCD parameter. If the OPTCD
parameter does not contain an F, feedback will be in the form of MBBCCHHR. If
you code an F in the OPTCD parameter, the format of the feedback depends on
the reference method used. Figure 52 provides details on reference methods
and feedback formats.
Figure 52. MVS Feedback Formats
Type or
Reference
Character-
istics
Relative
block
number
within the
data set.
You supply
key
Relative
track
number
and block
identifi-
cation.
Relative
track
number.
You supply
key in key
field.
Actual
device
address.
BBB TTR TT MBBCCHHR
Feedback
Format
Feedback
Format
Binary
value left
justified in
block
address
field.
TT=Track
number
(2-byte
binary
value)
R=Record
on track
(1-byte
binary
value)
Relative
track
number
(2-byte
binary
value)
Minimum
length
(bytes) of
Block-
address
field
3 3 2 8
OPTCD
=F
Relative
Address
Bytes
BBB
3
BBB
3
TTR
8
TTR
3
OPTCD
NOT
=F
Actual
Address
Bytes
MBBCCHHR
8
MBBCCHHR
8
MBBCCHHR
8
13.2.6.13 LIOCS Indexed Sequential Definition
Indexed sequential (ISAM) files should be converted to VSAM; that is, ISAM files
should not be used in MVS. VSE ISAM files should either be converted prior to
the migration to MVS (recommended) or during the conversion process.
326 VSE to OS/390 Migration Workbook