<2. Basic Design and Function Design>
TIP
In subsequent description, the term "retain data on the flash memory" refers to retain data which
was current as at the time when it was saved to the system card but not necessarily the most up-to-
date.
For instance, if retain data was saved a week ago, “retain data on the flash memory" would be one
week old.
● Behavior of Retain Data when FCN-500 or FCN-RTU Power is Off/On
1. If retain data is resident in non-volatile memory
As described earlier, retain data residing in non-volatile memory is retained even
after the FCN-500 or FCN-RTU is powered off. When the FCN-500 or FCN-RTU
is powered on, the system reboots using retain data in the non-volatile memory so
retain data persistency is guaranteed.
However, under certain circumstances, retain data in the non-volatile memory
may not be restored. Instead, all retentive variables are first initialized to their
initial values after power on. If retain data has been previously saved to the flash
memory, that data is restored. Otherwise, the FCN-500 or FCN-RTU reboots with
all initial variable values. Some circumstances under which retain data in the non-
volatile memory will not be restored are listed below.
• If the structure of retain data of the application at startup does not match
the structure of retain data in the non-volatile memory
If the control application running before power off is inconsistent with the boot
project on the flash memory on the number, data type or some other aspect of
retain data, retain data in the non-volatile memory will not be restored after
power on.
• If the backup battery was removed
If the backup battery is removed when power is off, retain data, like all other
data residing in the non-volatile memory, will be lost and hence cannot be
restored at power up.
• If the CPU module or FCJ has been replaced
If the CPU module or FCJ is replaced, retain data residing in the non-volatile
memory of the hardware naturally cannot be restored.
2. If retain data is resident in volatile memory
Retain data stored in volatile memory is lost when the FCN-500 or FCN-RTU is
powered off.
After power on, all retentive variables are first initialized to their initial values. If
retain data has been previously saved to the flash memory, that data is restored.
Otherwise, the FCN-500 or FCN-RTU reboots with all initial variable values.
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