DOS Fn 4403H: IOCTL Send Control Data to Character Device

                                                         Compatibility: 2.0+ 
 Expects: AX    4403H
          BX    file handle  (device only)
          CX    byte count (amount of data to send)
          DS:DX Address of buffer containing data to send
 Returns: AX    error code  if CF is set to CY
                Number of bytes actually sent (if no error)
    Info: Some character device drivers support this method of
          communicating with a device driver to select special features
          (such as setting the baud rate of a COM port).  The layout and
          contents of the control data varies from device to device.

   Notes: ■ This fn is supported only if bit 14 of the Device Attribute
            (the rDevAttr field of the driver's DevHdrRec structure) is
            set.  Use Fn 4400H to check this bit.

See Also: Fn 44H (IOCTL)
          Fn 4402H (Receive Control Data from Character Device)
          Fn 4405H (Send Control Data to Block Device)
          DOS Functions