Datasheet

Product data sheet Rev. 7 — 19 December 2014 44 of 86

NXP Semiconductors

PCF2129

Accurate RTC with integrated quartz crystal for industrial applications

8.11.4 Dependency between Battery switch-over and timestamp

The timestamp function depends on the control bit BTSE in register Control_3:

[1] Default value.

8.12 Interrupt output, INT

PCF2129 has an interrupt output pin INT which is open-drain, active LOW (requiring a

pull-up resistor if used). Interrupts may be sourced from different places:

• second or minute timer

• 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) 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, AF, TSFx, and BF can be cleared by command.

• The flag WDTF is read only. How it can be cleared is explained in Section 8.10.5.

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

circuit when the battery is replaced.

Table 71. Battery switch-over and timestamp

BTSE BF Description

[1]

the battery switch-over does not affect the

timestamp registers

1 If a battery switch-over event occurs:

[1]

the timestamp registers store the time and

date when the switch-over occurs;

after this event occurred BF is set logic 1

1 the timestamp registers are not modified;

in this condition subsequent battery

switch-over events or falling edges on pin TS

are not registered