Datasheet

Operation modes M48T35AV
12/29 Doc ID 6845 Rev 9
Also, as V
CC
rises, the battery voltage is checked. If the voltage is less than approximately
2.5 V, an internal battery not OK (BOK
) flag will be set. The BOK flag can be checked after
power up. If the BOK
flag is set, the first WRITE attempted will be blocked. The flag is
automatically cleared after the first WRITE, and normal RAM operation resumes. Figure 8
illustrates how a BOK
check routine could be structured.
For more information on battery storage life refer to the application note AN1012.
Figure 8. Checking the BOK
flag status
READ DATA
AT ANY ADDRESS
AI00607
IS DATA
COMPLEMENT
OF FIRST
READ?
(BATTERY OK)
POWER-UP
YES
NO
WRITE DATA
COMPLEMENT BACK
TO SAME ADDRESS
READ DATA
AT SAME
ADDRESS AGAIN
NOTIFY SYSTEM
OF LOW BATTERY
(DATA MAY BE
CORRUPTED)
WRITE ORIGINAL
DATA BACK TO
SAME ADDRESS
(BATTERY LOW)
CONTINUE