PCF2123TS datasheet(21/54 Pages) NXP

21 / 54 page

PCF2123_1

Product data sheet

Rev. 01 — 19 November 2008

21 of 54

NXP Semiconductors

PCF2123

SPI Real time clock/calendar

9.8.1 Minute and second interrupt

The minute and second interrupts (bits MI and SI) are pre-deﬁned timers for generating

periodic interrupts. The timers can be enabled independently from one another. However,

a minute interrupt enabled on top of a second interrupt will not be distinguishable since it

will occur at the same time; see Figure 14.

The minute and second ﬂag (bit MSF) is set to logic 1 when either the seconds or the

minutes counter increments according to the currently enabled interrupt. The ﬂag can be

read and cleared by the interface. The status of bit MSF does not affect the INT pulse

generation. If the MSF ﬂag is not cleared prior to the next coming interrupt period, an INT

pulse will still be generated.

The purpose of the ﬂag is to allow the controlling system to interrogate the PCF2123 and

identify the source of the interrupt i.e. minute or second, countdown timer or alarm.

In this example, TI_TP is set to logic 1 resulting in 1

⁄64 Hz wide interrupt pulse and the MSF ﬂag is

not cleared after an interrupt.

Fig 14. INT example for MI and SI

Table 26.

Effect of bits MI and SI on INT generation

Minute interrupt (bit MI)

Second interrupt (bit SI)

Result

no interrupt generated

an interrupt once per minute

an interrupt once per second

Table 27.

Effect of MI and SI on MSF

Minute interrupt (bit MI)

Second interrupt (bit SI)

Result

MSF never set

MSF set when minutes counter

increments

MSF set when seconds counter

increments

MSF set when seconds counter

increments

001aaf905

seconds counter

minutes counter

INT when SI enabled

MSF when SI enabled

INT when only MI enabled

MSF when only MI enabled

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