M48T201Y datasheet(22/33 Pages) STMICROELECTRONICS

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M48T201Y, M48T201V

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Battery Low Warning

The M48T201Y/V automatically performs battery

voltage monitoring upon power-up and at factory-

programmed time intervals of approximately 24

hours. The Battery Low (BL) Bit, Bit D4 of Flags

voltage is found to be less than approximately

2.5V. The BL Bit will remain asserted until comple-

tion of battery replacement and subsequent bat-

tery low monitoring tests, either during the next

power-up sequence or the next scheduled 24-hour

interval.

If a battery low is generated during a power-up se-

quence, this indicates that the battery is below ap-

proximately 2.5V and may not be able to maintain

data integrity in the SRAM. Data should be consid-

ered suspect and verified as correct. A fresh bat-

tery should be installed.

If a battery low indication is generated during the

24-hour interval check, this indicates that the bat-

tery is near end of life. However, data is not com-

promised due to the fact that a nominal VCC is

supplied. In order to insure data integrity during

subsequent periods of battery back-up mode, the

battery should be replaced. The SNAPHAT® top

may be replaced while VCC is applied to the de-

vice.

Note: This will cause the clock to lose time during

the interval the battery/crystal is removed.

The M48T201Y/V only monitors the battery when

a nominal VCC is applied to the device. Thus appli-

cations which require extensive durations in the

battery back-up mode should be powered-up peri-

odically (at least once every few months) in order

for this technique to be beneficial. Additionally, if a

battery low is indicated, data integrity should be

verified upon power-up via a checksum or other

technique.

Initial Power-on Defaults

Upon application of power to the device, the fol-

lowing register bits are set to a '0' state: WDS;

BMB0-BMB4; RB0-RB1; AFE; ABE; SQWE; W; R;

FT (see Table 9).

Table 9. Default Values

Note: 1. WDS, BMB0-BMB4, RB0, RB1.

2. State of other control bits undefined.

3. State of other control bits remains unchanged.

4. Assuming these bits set to '1' prior to power-down.

Condition

AFE

ABE

SQWE

WATCHDOG

Initial Power-up

(Battery Attach for SNAPHAT)(2)

000000

RESET(3)

000000

Power-down(4)

000111

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