Execute Direct Access Program: Difference between revisions

Revision as of 03:59, 8 May 2011

Revision as of 04:31, 8 May 2011

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The programmer is responsible for computing the full direct access record address, MBBCCHHR. System algorithms are available for calculating the MBBRRHHR from a TTRN. Additional system algorithms are available for calculating the TTRN from a record number.

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

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 structure within the XDAP macro expansion, as are the '''channel command words''' ('''CCW'''s).