Function  15h   Sequential Disk Write                                     (FCB) 
      Writes record specified by Struct -FCB sequentially to disk
entry   AH      15h 
	DS:DX	pointer to address of Struct -FCB
return  AL      00h     successful write 
		01h     diskette full, write canceled 
		02h     disk transfer area (DTA) too small or segment wrap 
note 1) The data to write is obtained from the disk transfer area 
     2) The record size is set to the value at offset 0Eh in the FCB. 
     3) This service cannot write to files set as read-only 
     4) The record pointed to by the Current Block (offset 0Ch) and the Current 
	Record (offset 20h) fields is loaded at the DTA, then the Current Block 
	and Current Record fields are incremented. 
     5) If the record size is less than a sector, the data in the DTA is written 
	to a buffer; the buffer is written to disk when it contains a full  
	sector of data, the file is closed, or a Reset Disk Int\21f\0D is
	issued. 
     6) The record is written to disk at the current DTA address as specified  
	by the most recent call to function 1Ah. If the size of the record and 
	location of the DTA are such that a segment overflow or wraparound would 
	occur, the error return is set to AL=02h