Your routine for writing output trailer labels receives control from data management's EOV or close routines. The EOV routine handles end-of-volume conditions (reflective strip or FEOV macro instruction). The close routine handles end-of-data-set conditions (CLOSE macro instruction). When your routine receives control, the tape has been positioned at the inter-record gap following the last written data set record.

Your routine does not need to reposition before returning control to the control program.

Your output trailer label routine is also given control when input data sets are closed. This allows you to position the tapes if necessary.

OPEN, EOV, and CLOSE will always turn the DEB31UCB on in the work area to signify that DXDEBUCB is a 31–bit UCB address. Although the UCB address field will be four bytes, it typically will contain a three-byte address. The modeset byte is moved from the DEBSDVM field to the DEBSDVMX field to enable 31 bit UCB addresses to be accommodated.