Datasheet

Product data sheet Rev. 6 — 11 July 2013 48 of 86

NXP Semiconductors

PCF2127AT

Integrated RTC, TCXO and quartz crystal

• watchdog timer

• alarm

• timestamp

• battery switch-over

• battery low detection

The control bit TI_TP (register Watchdg_tim_ctl) is used to configure whether the

interrupts generated from the second/minute timer (flag MSF in register Control_2) and

the countdown timer (flag CDTF in register Control_2) are pulsed signals or a

permanently active signal. All the other interrupt sources generate a permanently active

interrupt signal which follows the status of the corresponding flags. When the interrupt

sources are all disabled, INT

remains high-impedance.

• The flags MSF, CDTF, AF, TSFx, and BF can be cleared by command.

• The flag WDTF is read only. How it can be cleared is explained in Section 8.11.6.

• The flag BLF is read only. It is cleared automatically from the battery low detection

circuit when the battery is replaced.

8.13.1 Minute and second interrupts

Minute and second interrupts are generated by predefined timers. The timers can be

enabled independently from one another by the bits MI and SI in register Control_1.

However, a minute interrupt enabled on top of a second interrupt will not be

distinguishable since it will occur at the same time.

The minute/second flag MSF (register Control_2) is set logic 1 when either the seconds or

the minutes counter increments according to the enabled interrupt (see Table 54

). The

MSF flag can be read and cleared by command.

When MSF is set logic 1:

• If TI_TP is logic 1, the interrupt is generated as a pulsed signal.

• If TI_TP is logic 0, the interrupt is permanently active signal that remains until MSF is

cleared.

Table 54. Effect of bits MI and SI on pin INT and bit MSF

MI SI Result on INT Result on MSF

0 0 no interrupt generated MSF never set

1 0 an interrupt once per minute MSF set when minutes counter increments

0 1 an interrupt once per second MSF set when seconds counter increments

1 1 an interrupt once per second MSF set when seconds counter increments