- Entry:
- DSP
- VIT option:
- PSS
- Event:
- PAB dispatch
- VIT processing module:
- ISTRACPS
- Control is returned to:
- ISTAPCPD
The DSP entry marks the beginning of a PAB dispatch, which is the VTAM® major unit of work. This unit exists until terminated by an EXIT entry. While processing, it might wait for other events to complete (WAIT). It resumes processing with a RESM entry. The unit might be interrupted by a higher-priority task and continue when that task is finished.
Each PAB is identified by a unique index number. VTAM uses this number to find the called module and then creates a VIT entry for it.
To correlate all events associated with this unit, look
for the request parameter header (RPH) address, which is in many trace
records, and match it to the request parameter header (RPH) address
in the DSP trace record. This unit has exclusive use of that RPH until
EXIT. 
- Byte (hex)
- Contents
- 00–02
- Record ID: C"DSP"
- 03
- 0, or, for very extended PABs, PAB work element queue level dispatched
- 04
- ID is the primary address space ID (ASID). This field is 0 if the ASID is greater than X'FF'.
- 05
- Control block ID of work element (See z/OS Communications Server: SNA Diagnosis Vol 1, Techniques and Procedures.)
- 06
- PAB flag field (PABFLAGS)
- Bit
- Meaning
- 1... ....
- PAB is unconditionally scheduled.
- .1.. ....
- PAB closedown is in progress.
- ..1. ....
- PAB is synchronous.
- ...1 ....
- PAB extension is present.
- .... 1...
- Do not dequeue work element.
- .... .1..
- Do not detach the request parameter header (RPH).
- .... ..1.
- Indicates a very extended PAB.
- .... ...1
- Indicates a slightly extended PAB.
- 07
- PAB flag field (PABFLGS1)
- Bit
- Meaning
- 1... ....
- Switch the PST address of the major control block for this PAB to the new PST address contained in DYPNWPST.
- .1.. ....
- This PAB has a data space extension.
- ..1. ....
- This PAB's major control block is an FMCB.
- ...1 ....
- PAB can be referenced in PSW disable mode.
- .... 1...
- PAB is persistent.
- .... .1..
- APSTERM/APSINIT FMCB during PAB dispatch.
- .... ..xx
- Reserved.
- 08–0B
- PST address
- 0C–0F
- PAB address
- 10–13
- Address of work element most recently queued to the PAB
- 14–17
- Address of work element currently being dispatched
- 18–1B
- Module name abbreviation (bytes 4, 5, 7, and 8 of the module name) or PAB DVT address (high-order bit of X'18' = 0). For an explanation of the module-naming convention, see Using module names to isolate VTAM problems. (The module name might be unavailable if the PAB being scheduled is associated with an address space different from the current one.)
- 1C–1F
- Request parameter header (RPH) address