M48T212Y datasheet(20/32 Pages) STMICROELECTRONICS

20 / 32 page

M48T212Y, M48T212V

20/32

Battery Low Warning

The M48T212Y/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

is found to be less than approximately 2.5V. The

BL Bit will remain asserted until completion of bat-

tery replacement and subsequent battery 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 2.5 volts and may not be able to

maintain data integrity in the SRAM. Data should

be considered suspect and verified as correct. A

fresh battery 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® bat-

tery/crystal top should be replaced with VCC pow-

ering the device to avoid data loss.

Note: this will cause the clock to lose time during

the time interval the battery crystal is removed.

The M48T212Y/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 in-

tegrity 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, W, and FT

(see Tabel 10).

Table 10. 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

WATCHDOG

Initial Power-up

(Battery Attach for SNAPHAT)(2)

00000

RESET (3)

00000

Power-down (4)

01011

Subsequent Power-up

01000

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