Additional Information for TDF Presentation

Slide 5

The z/Architecture TRAP instruction, allows a privileged program, to create a control structure for redirection of program execution to a designated entry point. TDF uses this facility to interrupt the execution of the application program. It then uses a series of internal PC routines to provide the functionality used by the ISPF User Interface. When directed by the user, TDF resumes the application program execution until the next interrupt point occurs.

Since TDF does not use program check interrupts or z/OS Recovery Termination Manager (RTM) exits to gain control, it is not affected by the application’s RTM exits, regardless of the number or types of exits used. The dynamic nature of TDF allows a developer to debug complex, multi-tasking multiple address space servers without a single program modification.

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The TRAP instructions operates in all z/OS environments; task or SRB, locked or unlocked, enabled or disabled, cross memory, supervisor or problem, and AR or primary address space control (ASC) modes. The only environments not supported by the z/Architecture hardware are applications running in home ASC mode (SACF 768) or secondary ASC mode (SACF 256). These modes should not be confused with Access register mode using ALET values 1 and 2 to reference storage in the secondary and home address spaces, respectively. Secondary and Home Address space control modes are very rarely used.

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