Mitsubishi Electric MELSEC-Q00U(J)CPU User Manual page 51

(3) Program file structure
A program file consists of a file header, execution program, and reserved area for online change.
Program file structure
File header
Execution program
Reserved area for
online change
The sizes of the programs stored in the CPU module program memory are the total of above three areas.
Item
File header
Execution program
Reserved area for
online change
37 steps (default)
(39 steps (Q50/Q100UDEHCPU))
500 steps
This area stores data such as the name, size, and created date of files. The file header size
ranges from 25 to 41 steps (100 to 164 bytes) depending on the setting made in the Device tab of
the PLC Parameter dialog box.
This area stores the created program.
This area is used when the number of steps is increased after writing data in the RUN status.
(Default: 500 steps (2000 bytes) The setting value can be changed in the "Program Detail Setting"
dialog box. (It can be changed while online change is performed.) After the online change is
complete, remaining number of steps for this area is displayed.
CHAPTER 2 APPLICATION OF PROGRAMMING
These areas are reserved
in increments of file size units.
Page 44, Section 2.1.3
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