Open File

Expects: AH    3dH
         AL    Access Mode (0=read, 1=write, 2=both, etc.)
         DS:DX address of an ASCIIZ- string of a filespec-
         -----------------------------------------------------------------
Returns: AX    error code if CF is set to CY
               file handle if no error
         -----------------------------------------------------------------
   Info: Opens an existing file for read and/or write operations.

   DS:DX points to an ASCIIZ string in the form...
            d:\path\filename.ext 0 
         ...which identifies the location and name of the file to open.
         If drive and/or path are omitted, defaults are assumed.

         If CF is set on return, an error code is in AX and no action was
         taken.

  Notes: _ The file must exist.  See Fn 3cH (create file).

	Close File

 Expects: AH    3eH
          BX    file handle
          -----------------------------------------------------------------
 Returns: AX    error code if CF is set to CY
          -----------------------------------------------------------------
    Info: Closes an open file.

       BX contains a file handle returned from an Open operation.  The file
          represented by that handle is closed, its buffers are flushed,
          and the directory is updated with the correct size, time, and
          date.

          Because of the potential shortage of file handles (default=8,
          max=20 with DOS < 3.3), you may want to close one or more of the
          default handles, such as handle 3 (Standard AUX).


Si eventual:

	Seek File

Expects: AH    42H
         BX    file handle
         CX:DX distance to move file pointer: offset is (CX * 65536) + DX
         AL    subfn: 0 = move pointer to start of file + CX:DX
                      1 = move pointer to current position + CX:DX
                      2 = move pointer to end of file + CX:DX
         -----------------------------------------------------------------
Returns: AX    error code if CF is set to CY
         DX:AX new position of file read/write pointer (if no error)
         -----------------------------------------------------------------
   Info: This moves the logical read/write pointer to the desired address.
         All file reads and writes will start from the new address.