6 - 1 6 - 1
MELSEC-Q
6 I/O Processing of Data Files
6
6 I/O PROCESSING OF DATA FILES
The following two types of data files can be creating by BASIC. These files have the
following characteristics.
• Sequential Files
Data are written in a file continuously. This allows data to be saved on memory cards
and FD without wasting space, but portions that are only required cannot be read and
written.
Sequential files are like data stored on a tape.
It is convenient to read data from the beginning,
but data in between cannot be read and written
by a single access.
• Random Files
Data is written on separate blocks. This allows a required portion of the data to be
read and written. However, wasted space will be created if data that is smaller than a
block is saved.
Random file
Random files are like data stored on a
CD. Data in between can be read and
written by a single access.
REMARK
Data in sequential files and random files can be used with one another, but note the
following.
• When data from a sequential file is used as a random file, be sure that the data
from the sequential file is correctly corresponding to the field of the random file.
• When data from a random file is used as a sequential file, carefully evaluate the
handling of characters in the random file data that are used as separator symbols
for sequential files.
For details on separator symbols for sequential files, see Section 6.2.
