PCF2127TSLASH2Y datasheet(48/100 Pages) PHILIPS

48 / 100 page

PCF2127

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Product data sheet

Rev. 8 — 19 December 2014

48 of 100

NXP Semiconductors

PCF2127

Accurate RTC with integrated quartz crystal for industrial applications

8.12 Timestamp function

The PCF2127 has an active LOW timestamp input pin TS, internally pulled with an

on-chip pull-up resistor to Voper(int). It also has a timestamp detection circuit which can

detect two different events:

1. Input on pin TS is driven to an intermediate level between power supply and ground.

2. Input on pin TS is 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_ctl).

A most common application of the timestamp function is described in Ref. 3 “AN11266”.

See Section 8.13.6 for a description of interrupt generation from the timestamp function.

8.12.1 Timestamp flag

1. When the TS input pin is driven to an intermediate level between the power supply

and ground, either on the falling edge from VDD or on the rising edge from ground,

then the following sequence occurs:

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

b. The timestamp flag TSF1 (register Control_1) is set.

c. If the TSIE bit (register Control_2) is active, an interrupt on the INT pin is

generated.

The TSF1 flag can be cleared by command. Clearing the flag clears the interrupt.

Once TSF1 is cleared, it will only be set again when a new negative or positive edge

on pin TS is detected.

2. When the TS input pin is driven to ground, the following sequence occurs:

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

b. In addition to the TSF1 flag, the TSF2 flag (register Control_2) is set.

(1) When using switches or push-buttons, it is recommended to connect a 1 nF capacitance to the TS

pin to ensure proper switching.

Fig 26. Timestamp detection with two push-buttons on the TS pin (for example, for

tamper detection)

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