Clock operation

M48T201Y, M48T201V

24/37

Figure 10.

Crystal accuracy across temperature

Figure 11.

Calibration waveform

3.11

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 register 7FFF0h, will be asserted if the battery voltage is found to be less than

approximately 2.5 V. The BL bit will remain asserted until completion of battery 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 sequence, this indicates that the battery is

below approximately 2.5 V 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.

AI00999

–160

0

10203040506070

Frequency (ppm)

Temperature

°C

80

–10

–20

–30

–40

–100

–120

–140

–40

–60

–80

20

0

–20

ΔF

= -0.038

(T - T

F

ppm

C

2

T

AI00594B

NORMAL

POSITIVE

CALIBRATION

NEGATIVE

CALIBRATION