To initiate physical-sequential access, either specify DSN=0, or do not specify the DSN parameter at all. To begin the read, initialize the argument field in the first buffer list entry to zero or to the argument of the DSCB. If the argument is zero, CVAF uses the argument of the start of the VTOC.

The ACCESS keyword determines whether CVAF reads the DSCB whose argument is supplied or the DSCB following it. For example, to read the first DSCB (the format-4 DSCB) in the VTOC, you can set the BFLEARG in the first buffer list entry to zero and specify ACCESS=GTEQ in the CVAFSEQ macro. If you subsequently specify ACCESS=GT, CVAF reads the second DSCB (the first format-5 DSCB). Set the DSCB size to 140 in buffer list entries.

If your program is authorized, CVAF reads as many DSCBs as there are entries in the buffer list for a single CVAF call; if it is not authorized, CVAF reads only one DSCB.

CVAF uses one buffer list and does not inspect a second buffer list chained from the first. If your program is authorized, CVAF uses all entries in the buffer list; if it is not authorized, CVAF uses only the first entry. CVAF does not inspect the skip bit. Each entry must contain a buffer address and have the length field set to 140. CVAF updates the argument field of each buffer list entry with the argument of the DSCB. You can specify the argument format by setting either the TTR or CCHHR bit in the buffer list entry to 1. If neither bit is set, CVAF returns a CCHHR argument.

CVAF uses only the argument in the first entry to begin the search and does not inspect arguments in subsequent entries. If you specify a nonzero argument value in the first entry, there must be a DSCB with that argument.

CVAF indicates an end-of-data condition by providing return code 4 in register 15, and a value of X'20' in the CVSTAT field. CVAF sets the argument fields of all buffer list entries following the last DSCB read, to zero (the first entry is zero if CVAF does not read any DSCBs).

CVAF reads all DSCBs, including format-0 DSCBs. You cannot be certain that you have read all DSCBs until CVAF has read the entire VTOC. For a nonindexed VTOC, the DS4HPCHR field of the format-4 DSCB contains the CCHHR of the last format-1 DSCB. DSCBs other than format-1 can reside beyond that location. For an indexed VTOC, the VMDS contains information about which DSCBs are format-0 DSCBs.

For physical-sequential access, a CVAFSEQ request to an extended address volume will fail if the EADSCB=OK indicator is not set. CVAF return code of 4 with a CVAF status code (CVSTAT) of STAT082 will be set.