Omron CJ1G-CPUxx, Instructions Manual

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File Memory Instructions Section 3-26
will not be able to use the Memory Card even if it is reformatted in the CPU
Unit.
Number of Files in Root Directory
There is a limit to the number of files that can be placed in the root directory of
a Memory Card (just as there is a limit for a hard disk). Although the limit
depends on the type and format of the Memory Card, it will be between 128
and 512 files. When using applications that write log files or other files at a
specific interval, write the files to a subdirectory rather than to the root direc-
tory.
Subdirectories can be created on a computer or by using the CMND(490)
instruction. Refer to 3-25-4 DELIVER COMMAND: CMND(490) for a specific
example using CMND(490).
Number of Writes
Generally speaking, there is no limit to the number of write operations that can
be performed for a flash memory. For the Memory Cards, however, a limit of
100,000 write operations has been set for warranty purposes. For example, if
the Memory Card is written to every 10 minutes, over 100,000 write opera-
tions will be performed within 2 years.
Minimum File Size
If many small files, such as ones containing only a few words of DM Area
data, are stored on the Memory Card, it will not be possible to use the com-
plete capacity of the Memory Card. For example, if a Memory Card with an
allocation unit size of 4,096 bytes is used, at least 4,096 bytes of memory will
be used for each file regardless of how small the file is. If you save 10 words
of DM Area data to the Memory Card, 4,096 bytes of memory will be used
even though the actual file size is only 68 bytes. Using files of such a small
size greatly reduces the utility rate of the Memory Card. If the allocation unit
size is reduced to increase the utility rate, however, the access speed will be
reduced.
The allocation unit size of the Memory Card can be checked from a DOS
prompt using CHKDSK. The specific procedure is omitted here. Refer to gen-
eral computer references for more information on allocation unit sizes.
Memory Card Access Precautions
When the PLC is accessing the Memory Card, the BUSY indicator will light on
the CPU Unit. Observe the following precautions.
1,2,3... 1. Never turn OFF the power supply to the CPU Unit when the BUSY indica-
tor is lit. The Memory Card may become unusable if this is done.
2. Never remove the Memory Card from the CPU Unit when the BUSY indi-
cator is lit. Press the Memory Card power OFF button and wait for the
BUSY indicator to go out before removing the Memory Card. The Memory
Card may become unusable if this is not done.
3. Insert the Memory Card with the label facing to the right. Do not attempt to
insert it in any other orientation. The Memory Card or CPU Unit may be
damaged.
4. A few seconds will be required for the CPU Unit to recognize the Memory
Card after it is inserted. When accessing a Memory Card immediately after
turning ON the power supply or inserting the Memory Card, program an
NC condition for the Memory Card Recognized Flag (A34315) as an input
condition, as shown below.