M48T129YPM datasheet(14/22 Pages) STMICROELECTRONICS

14 / 22 page

M48T129Y, M48T129V

14/22

Figure 12. Alarm Interrupt Reset Waveform

Figure 13. Back-up Mode Alarm Waveforms

AI02581

AD0-AD7

ACTIVE FLAG BIT

ADDRESS 1FF0h

IRQ/FT

HIGH-Z

15ns Min

AI01678C

VCC

IRQ/FT

HIGH-Z

VPFD (max)

VPFD (min)

AFE bit in Interrupt Register

AF bit in Flags Register

HIGH-Z

VSO

tREC

Calibration values, including the number of sec-

onds lost or gained in a given period, can be found

in Application Note: TIMEKEEPER CALIBRA-

TION. This allows the designer to give the end

user the ability to calibrate the clock as the envi-

ronment requires, even if the final product is pack-

aged in a non-user serviceable enclosure. The

designer could provide a simple utility that access-

es 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 1FFF9h) is ’0’,the Frequency

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

Enable bit (AFE, D7 of 1FFF6h) is ’0’, and the

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

or the Watchdog Register (1FFF7h=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.

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