Execute Direct Access Program: Difference between revisions

Revision as of 00:42, 8 May 2011

Revision as of 03:59, 8 May 2011

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List and Execute forms of XDAP are provided, whereby a prototype form, called the List Form, is coded as data, and a functional form, called the Execute Form, is coded as instructions. XDAP is also provided in a conventional form, in which case the two forms are combined.

XDAP results in an SVC 0 instruction, the EXCP supervisor call, being executed, hence '''Execute Channel Program''' ('''EXCP''') is implicitly embedded within XDAP. The IOB, which is the sole parameter to EXCP, is included as a data structrestructure within the XDAP macro expansion, as are the '''channel command words''' ('''CCW'''s).

XDAP must reference an OPENed DCB and a full direct access record address. The DCB may be OPENed for input, for output or for input/output, but all outputs must be update writes of existing records as XDAP does not support format writes. BSAM and BPAM are available for executing format writes (writes which add new records to the dataset).