Drive Memory Defragmentation (For Other Station Qnacpu) - Mitsubishi MELSEC Q Series Reference Manual

3.7 Drive Memory Defragmentation (for Other Station QnACPU)

16th cluster from
the head cluster
Last cluster (number n)
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3 WHEN COMMUNICATING USING THE QnA COMPATIBLE 3E/3C/4C FRAMES OR 4E FRAME
An external device uses this function to perform the following operations on the
QnACPU drive of another station that stores the program file containing the
parameters and sequence programs.
(1) Reading status of drive memory usage
Checks the status of the drive memory usage (cluster usage status) of the
designated drive.
(2) Drive memory defragmentation
Increases the contiguous free drive space by defragmenting the drive memory
into cluster units when the memory areas containing valid data are scattered
throughout the drive memory.
POINT
A cluster is the minimum unit when files are stored to drive memory (memory cards,
etc.) and the memories containing data are managed by FAT( 1).
The size of one cluster of each QnACPU drive is shown below:
• Internal memory :
• Other memory
For example, if an amount of data less than 512 bytes is written to a memory card,
one cluster of drive memory is used to write the data.
If 513 to 1024 bytes of data are written, two clusters of drive memory is used to
write the data.
1 FAT (File Allocation Table)
Table used by the OS to manage the location of files in the drive memory.
(Illustration of drive memory defragmentation)
Head cluster (number 0)
(Before drive memory
defragmentation)
: Corresponding cluster is being used (valid data is written in it)
: Corresponding cluster in not used (free)
4096 bytes
: 512 bytes
(After drive memory defragmentation)
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