PCF2123 datasheet(11/54 Pages) NXP

11 / 54 page

PCF2123_1

Product data sheet

Rev. 01 — 19 November 2008

11 of 54

NXP Semiconductors

PCF2123

SPI Real time clock/calendar

9.3.2 Register Control_2

9.4 OS ﬂag

The PCF2123 includes a ﬂag (bit OS) which is set whenever the oscillator is stopped (see

Figure 8 and Figure 9). The ﬂag will remain set until cleared by software. If the ﬂag cannot

be cleared, then the PCF2123 oscillator is not running. This method can be used to

monitor the oscillator and to determine if the supply voltage has reduced to the point

where oscillation fails.

Table 6.

Bit

Symbol

Value

Description

Reference

minute interrupt is disabled

Section 9.8.1

minute interrupt is enabled

second interrupt is disabled

second interrupt is enabled

MSF

no minute or second interrupt generated

ﬂag set when minute or second interrupt

generated;

ﬂag must be cleared to clear interrupt

when TI_IP = 0

TI_TP

interrupt pin follows timer ﬂags

Section 9.9.2

interrupt pin generates a pulse

no alarm interrupt generated

Section 9.7.1

ﬂag set when alarm triggered;

ﬂag must be cleared to clear interrupt

no countdown timer interrupt generated

ﬂag set when countdown timer interrupt

generated;

ﬂag must be cleared to clear interrupt

when TI_IP = 0

AIE

no interrupt generated from the alarm ﬂag

Section 9.9.3

interrupt generated when alarm ﬂag set

TIE

no interrupt generated from the countdown

timer

Section 9.9.2

interrupt generated by the countdown timer

Fig 8.

OS set by failing VDD

001aai561

VDD

VOSC(MIN)

battery operation

main supply

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