Mitsubishi Electric MELSEC Q Series User Manual page 332

(4) Battery backup RAM / Standard RAM
(a) Battery backup RAM
A battery backup RAM is a memory that stores data that need to be retained through power OFF among data
used by user programs, etc.
Access to a battery backup RAM from the C Controller module dedicated function by using the user program is
allowed. Functions used are indicated below.
Function name
CCPU_WriteSRAM
CCPU_ReadSRAM
CCPU_WriteSRAM_ISR
CCPU_ReadSRAM_ISR
Remark
For C Controller module dedicated function, refer to the following.
Page 353, CHAPTER 20
A battery backup RAM cannot store files. To store files, create a standard RAM area within a battery backup
RAM.
(b) Standard RAM
The area for standard RAM is created by specifying the memory capacity in the battery backup RAM with
parameters.
As with a standard ROM, it can be accessed from FTP, Telnet and user programs and store files.
Use the following functions in Setting/monitoring tools for the C Controller module to set a memory capacity of
a standard RAM.
•
Project view  "Parameter"  "CCPU Parameter"  <<System settings>>  "Standard RAM
settings"
● A standard RAM is created when the set parameters are applied (power OFFON /reset).
● When the area for standard RAM is created, the memory specified for standard RAM is occupied, therefore, the battery
backup RAM area will be decreased.
[Example] If a 2MB standard RAM is created
● Before modifying the standard RAM setting, it is recommended to backup the standard RAM data. When the standard
RAM setting is modified, the standard RAM area is cleared to 0.
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Writes data to the battery backup RAM.
Reads data from the battery backup RAM.
Writes data to the battery backup RAM.
Executable from the interrupt service routine.
Reads data from the battery backup RAM.
Executable from the interrupt service routine.
5MB (total capacity) - 2MB (standard RAM capacity) = 3MB (available battery backup RAM capacity)
Function