UPD78F0411GA-GAM-AX Datasheet, PDF (526/564 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

CHAPTER 24 FLASH MEMORY
24.8.1 Boot swap function
If rewriting the boot area has failed during self-programming due to a power failure or some other cause, the data
in the boot area may be lost and the program may not be restarted by resetting.
The boot swap function is used to avoid this problem.
Before erasing boot cluster 0^Note, which is a boot program area, by self-programming, write a new boot program to
boot cluster 1 in advance. When the program has been correctly written to boot cluster 1, swap this boot cluster 1 and
boot cluster 0 by using the set information function of the firmware of the 78K0/LC3, so that boot cluster 1 is used as a
boot area. After that, erase or write the original boot program area, boot cluster 0.
As a result, even if a power failure occurs while the boot programming area is being rewritten, the program is
executed correctly because it is booted from boot cluster 1 to be swapped when the program is reset and started next.
If the program has been correctly written to boot cluster 0, restore the original boot area by using the set
information function of the firmware of the 78K0/LC3.
Note A boot cluster is a 4 KB area and boot clusters 0 and 1 are swapped by the boot swap function.
Boot cluster 0 (0000H to 0FFFH): Original boot program area
Boot cluster 1 (1000H to 1FFFH): Area subject to boot swap function
XXXXH
Figure 24-13. Boot Swap Function
User program
Self programming
to boot cluster 1
User program
Setting of boot flag
User program
2000H
1000H
User program
Boot program
0 0 0 0 H ^{(boot cluster 0)}
Boot
New boot program
(boot cluster 1)
Boot program
(boot cluster 0)
Boot
New boot program
(boot cluster 1)
Boot
Boot program
(boot cluster 0)
XXXXH
Self programming
to boot cluster 0
User program
Setting of boot flag
User program
2000H
New boot program
(boot cluster 1)
1000H
Boot
New boot program
0 0 0 0 H ^{(boot cluster 0)}
New boot program
(boot cluster 1)
New boot program
(boot cluster 0)
Boot
Remark Boot cluster 1 becomes 0000H to 0FFFH when a reset is generated after the boot flag has been set.
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User’s Manual U18698EJ1V0UD