IBM SC33-1683-02 - Manual (Page 71)

DBCTL interface control program exit XXDFA
When invoked
By an active CICS when its connection to DBCTL fails. Your exit program is
invoked after the active CICS has informed the alternate CICS of the
failure.
Exit-specific parameters
UEPDBXR
Address of CICS XRF information for use with DBCTL. The CICS
XRF information can be mapped using the DSECT DFHDXUEP.
Return codes
UERCNOAC
Take no action.
UERCSWCH
Switch to the alternate DBCTL.
UERCABNO
Abend CICS without a dump.
UERCABDU
Abend CICS with a dump.
XPI calls
TRANSACTION_DUMP must not be used.
DBCTL interface control program exit
Chapter 1. Global user exit programs 39