Datasheet

PCF2129 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 7 — 19 December 2014 22 of 86
NXP Semiconductors
PCF2129
Accurate RTC with integrated quartz crystal for industrial applications
8.6 Oscillator stop detection function
The PCF2129 has an on-chip oscillator detection circuit which monitors the status of the
oscillation: whenever the oscillation stops, a reset occurs and the oscillator stop flag OSF
(in register Seconds) is set logic 1.
• Power-on:
a. The oscillator is not running, the chip is in reset (OSF is logic 1).
b. When the oscillator starts running and is stable after power-on, the chip exits from
reset.
c. The flag OSF is still logic 1 and can be cleared (OSF set logic 0) by command.
• Power supply failure:
a. When the power supply of the chip drops below a certain value (V
low
), typically
1.2 V, the oscillator stops running and a reset occurs.
b. When the power supply returns to normal operation, the oscillator starts running
again, the chip exits from reset.
c. The flag OSF is still logic 1 and can be cleared (OSF set logic 0) by command.
Fig 10. Typical driving capability of V
BBS
: (V
BBS
 V
DD
) with respect to the output load
current I
BBS
,
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