PCF2123U datasheet(21/63 Pages) NXP

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PCF2123

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Product data sheet

Rev. 5 — 27 April 2011

21 of 63

NXP Semiconductors

PCF2123

SPI Real time clock/calendar

The minute and second flag (bit MSF) is set 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.

The duration of both of these timers will be affected by the register Offset_register (see

Section 8.9). Only when the Offset_register has the value 00h the periods will be

consistent.

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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