JCL for Processing with the ISAM Interface

To process a key-sequenced data set, replace the ISAM DD statement with a VSAM DD statement using the ddname that was used for ISAM. The VSAM DD statement names the key-sequenced data set and gives any necessary VSAM parameters (through AMP). Specify DISP=MOD for resume loading and DISP=OLD or SHR for all other processing. You do not have to specify anything about the ISAM interface itself. The interface is automatically brought into action when your processing program opens a DCB whose associated DD statement describes a key-sequenced data set (instead of an indexed sequential data set).

The DCB parameter in the DD statement that identifies a VSAM data set is nonvalid and must be removed. If the DCB parameter is not removed, unpredictable results can occur. Certain DCB-type information can be specified in the AMP parameter.

Table 1 shows the DCB fields supported by the ISAM interface.

Table 1. DCB fields supported by ISAM interface
Field Name	Meaning
BFALN	Same as in ISAM; defaults to a doubleword
BLKSI	Set equal to LRECL if not specified
BUFCB	Same as in ISAM
BUFL	The greater value of AMDLRECL or DCBLRECL if not specified
BUFNO	For QISAM, one; for BISAM, the value of STRNO if not specified
DDNAM	Same as in ISAM
DEBAD	During the DCB exit, contains internal system information; after the DCB exit, contains the address of the dummy DEB built by the ISAM interface
DEVT	Set from the VSAM UCB device type code
DSORG	Same as in ISAM
EODAD	Same as in ISAM
ESETL	Address of the ISAM interface ESETL routine (see Table 1)
EXCD1	See the QISAM exception codes
EXCD2	See the QISAM exception codes
EXLST	Same as in ISAM (except that VSAM does not support the JFCBE exit)
FREED	Address of the ISAM-interface dynamic buffering routine
GET/PUT	For QISAM LOAD, the address of the ISAM-interface PUT routine; for QISAM SCAN, 0, the address of the ISAM-interface GET routine; 4, the address of the ISAM-interface PUTX routine; and 8, the address of the ISAM-interface RELSE routine
KEYLE	Same as in ISAM
LRAN	Address of the ISAM-interface READ K/WRITE K routine
LRECL	Set to the maximum record size specified in the access method services DEFINE command if not specified (adjusted for variable-length, fixed, unblocked, and RKP=0 records)
LWKN	Address of the ISAM-interface WRITE KN routine
MACRF	Same as in ISAM
NCP	For BISAM, defaults to one
NCRHI	Set to a value of 8 before DCB exit
OFLGS	Same as in ISAM
OPTCD	Bit 0 (W), same as in ISAM; bit 3 (I), dummy records are not to be written in the VSAM data set; bit 6 (L), VSAM-deleted records (X'FF') are not read; dummy records are to be treated as in ISAM; all other options ignored
RECFM	Same as in ISAM; default to unblocked, variable-length records
RKP	Same as in ISAM
RORG1	Set to a value of 0 after DCB exit
RORG2	Set to a value of X'7FFFF' after DCB exit
RORG3	Set to a value of 0 after DCB exit
SETL	For BISAM, address of the ISAM-interface CHECK routine; for QISAM, address of the ISAM-interface SETL routine
ST	Bit 1 (key-sequence check), same as in ISAM; bit 2 (loading has completed), same as in ISAM
SYNAD	Same as in ISAM
TIOT	Same as in ISAM
WKPT1	For QISAM SCAN, WKPT1 +112=address of the W1CBF field pointing to the current buffer
WKPT5	Address of an internal system control block
WKPT6	For QISAM LOAD, address of the dummy DCB work area vector pointers; the only field supported is ISLVPTRS+4=pointer to KEYSAVE

When an ISAM processing program is run with the ISAM interface, the AMP parameter enables you to specify:

That a VSAM data set is to be processed (AMORG)
The need for additional data buffers to improve sequential performance (BUFND)
The need for extra index buffers for simulating the residency of the highest level(s) of an index in virtual storage (BUFNI)
Whether to remove records flagged (OPTCD)
What record format (RECFM) is used by the processing program
The number of concurrent BISAM and QISAM (basic and queued indexed-sequential access methods) requests that the processing program can issue (STRNO)
The name of an ISAM user exit routine to analyze physical and logical errors (SYNAD).

For a complete description of the AMP parameter and its syntax, see z/OS MVS JCL Reference.