Page Comparison

IN:
     HL = 0,1,2; not allowed (B=0)
     BHL = pointer to name of filename to open
     (B = 0, identified as local pointer)

     DE = 0,1,2; not allowed
     DE = pointer to space to insert explicit filename
     C = maximum space to fill with this explicit filename (e.g. 18)

     A = access mode
          OP_IN ($01)  = open for input
          OP_OUT ($02) = open for output
          OP_UP ($03)  = open for update (read/write)
          OP_MEM ($04) = open memory (internal usage - not for applications)
          OP_DIR ($05) = create directory - returns DOR handle
          OP_DOR ($06) = return DOR information - returns DOR handle

OUT, if call successful:
     Fc = 0
     IX = file handle for open file
     A(IN=OP_DOR): A = DOR type; DN_FIL, DN_EPR, Dn_DIR, etc.
     B = number of segments in the explicit filename
     C = number of characters in returned, expanded filename at (DE)
     DE = points beyond the last character of explicit filename

OUT, if call failed:
     Fc = 1
     A = error code:
          RC_BAD ($04), bad arguments
          RC_IVF ($17), invalid filename, eg. ".wrong"
          RC_ONF ($12), file not found
          RC_USE ($15), file already in use
          RC_FTM ($18), file type mismatch
          RC_UNK ($03), unknown request, eg. A(in) invalid

Registers changed after return:
     ......HL/..IY same
     AFBCDE../IX.. different