Specifies the address of a routine to receive control when a
    Change Mode to User or Change Mode to Supervisor instruction trap
    occurs.

    Format

      SYS$DCLCMH  addres ,[prvhnd] ,[type]

    C Prototype

      int sys$dclcmh  (int (*addres)(__unknown_params), void

                      *(*(prvhnd)), char type);