Function 03h    Write Data Blocks to Cassette		(PC, PCjr only) 
entry   AH      03h 
	CX      count of bytes to write 
	ES:BX   pointer to data buffer 
return  CF      set on error 
		AH      error code (see Int15f02)
	CX      0 
	ES:BX   pointer to last byte written+1 
note 1) NOP for systems where cassette not supported 
     2) The last block is padded to 256 bytes with zeroes if needed 
     3) No errors are returned by this service