M48T513V datasheet(15/23 Pages) STMICROELECTRONICS

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M48T513Y, M48T513V

Table 12. Alarm Repeat Mode

RPT4

RPT3

RPT2

RPT1

Alarm Activated

1111

Once per Second

1110

Once per Minute

1100

Once per Hour

1000

Once per Day

1000

Once per Month

This allows the designer to give the end user the

ability to calibrate the clock as the environment re-

quires, even if the final product is packaged in a

non-user serviceable enclosure. The designer

could provide a simple utility that accesses the

Calibration byte.

The second approach is better suited to a manu-

facturing environment, and involves the use of the

IRQ/FT pin. The pin will toggle at 512Hz, when the

Stop bit (ST, D7 of 7FFF9h) is ’0’, the Frequency

Test bit (FT, D6 of 7FFFCh) is ’1’, the Alarm Flag

Enable bit (AFE, D7 of 7FFF6h) is ’0’, and the

Watchdog Steering bit (WDS, D7 of 7FFF7h) is ’1’

or the Watchdog Register (7FFF7h = 0) is reset.

Note: A 4 second settling time must be allowed

before reading the 512Hz output.

Any deviation from 512Hz indicates the degree

and direction of oscillator frequency shift at the test

temperature.

For

example,

reading

512.010124Hz would indicate a +20 ppm oscillator

frequency error, requiring a –10 (WR001010) to be

loaded into the Calibration Byte for correction.

Note that setting or changing the Calibration Byte

does not affect the Frequency test output frequen-

cy.

The IRQ/FT pin is an open drain output which re-

quires a pull-up resistor for proper operation. A

500-10k

Ω resistor is recommended in order to

control the rise time. The FT bit is cleared on pow-

er-up.

BATTERY LOW WARNING

The M48T513Y/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.

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.

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.

The M48T513Y/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.

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, R and FT.

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