PCF2131 datasheet(39/85 Pages) NXP

39 / 85 page

NXP Semiconductors

PCF2131

Nano-power highly accurate RTC with integrated quartz crystal

Bit

Control_2

0[1]

Table 62. Example to clear only AF (bit 4)

[1]

The bits labeled as - have to be rewritten with the previous values.

Bit

Control_2

0[1]

Table 63. Example to clear only MSF (bit 7)

[1]

The bits labeled as - have to be rewritten with the previous values.

7.12 Timestamp function

The PCF2131 has four active LOW timestamp input pins TS1, TS2, TS3 and TS4, internally pulled with on-chip

pull-up resistors to Voper(int). It also has a timestamp detection circuit which can detect the event when inputs on

pin TS1/2/3/4 are driven to ground.

The timestamp function is enabled by default after power-on and it can be switched off by setting the control bit

TSOFF (register Timestp_ctl1/2/3/4).

The time recorded in the time stamps, when in 100 Hz disable mode (1 Hz mode), will be at least two 16 Hz

clocks behind the timestamp event and no more than 3 clocks behind. If the exact time of the timestamp event

is required then subtract 2 subseconds from the timestamp value and the result will have -0 subseconds to +1

subseconds of uncertainty.

A most common application of the timestamp function is described in [1].

See Section 7.13.5 for a description of interrupt generation from the timestamp function.

7.12.1 Timestamp flag

1. When the TS1/2/3/4 input pin are driven to ground, the following sequence occurs:

a. The actual date and time are stored in the timestamp registers.

b. The timestamp flag TSF1/2/3/4 flag is set.

c. If the TSIE1/2/3/4 bit is active, and corresponding interrupt mask is disabled, an interrupt on the INTA/B

pin is generated.

The TSF1/2/3/4 and TSF1/2/3/4_2 flags can be cleared by command; clearing the flag clears the interrupt.

Once TSF1/2/3/4 is cleared, it will only be set again when TS1/2/3/4 pin is driven to ground once again.

7.12.2 Timestamp mode

The timestamp function has two different modes selected by the control bit TSM (timestamp mode) in register

Timestp_ctl:

• If TSM is logic 0 (default): in subsequent trigger events without clearing the timestamp flags, the last

timestamp event is stored

• If TSM is logic 1: in subsequent trigger events without clearing the timestamp flags, the first timestamp event

is stored

PCF2131

All information provided in this document is subject to legal disclaimers.

Product data sheet

Rev. 2.0 — 5 October 2023

39 / 85

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