INT E0 - DR Multiuser DOS - "A_ATTACH" - ATTACH AUX DEVICE
        CL = A5h
Desc:   attaches the default auxiliary device to the calling process unless
          it is already attached to another process, in which case the call
          blocks until the device becomes available
Note:   this call should be used before attempting to read or write from
          the AUX device; however, the I/O calls internally call this function
          to ensure device ownership
SeeAlso: INT E0/CL=03h,INT E0/CL=04h,INT E0/CL=A6h,INT E0/CL=A7h,INT E0/CL=A8h