INT 13h,  16h (22)       Change Line Status                              many

    This service reports whether or not a diskette has been changed (disk
    drive door opened) since the last disk access. This service can be
    performed on diskettes only.

       On entry:      AH         16h
                      DL         Drive number (Bit 7 must be clear)

       Returns:       AH         Change Line Status (See below)
                      CF         Set if AH is not 0; otherwise cleared

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       Notes:         This service is not available for PCs, PCjrs, and
                      XTs dated before 1/10/86.

                      Use Service 15h to determine if a drive supports
                      change line detection.

                      If the Carry Flag is set and AH is 01h or 80h, then
                      an error has occurred. If AH is 06h, the Carry Flag
                      will be set, but that does not signal an error;
                      instead it means the "Diskette change" signal is
                      active (as shown below).

                         Change Line Status
                           AH       Meaning
                           00h      "Diskette change" signal not active
                           01h      Invalid diskette parameter         (ERROR)
                           06h      "Diskette change" signal active
                           80h      Drive not ready                    (ERROR)

                      For the AT, XT-286, and PC Convertible, the BIOS
                      executes INT 15h, Service 90h (Device Busy), for the
                      diskette (Type = 01h) prior to waiting for the
                      interrupt. INT 15h, Service 91h (Interrupt
                      Complete), is executed upon completion. Diskette
                      operations that require the diskette motor to be on
                      will call INT 15h, Service 90 (Device Busy), with
                      the type equal to "Diskette Drive Motor Start" (Type
                      = FDh). This allows the system to perform another
                      task while the drive motor is waiting to get up to
                      speed.