PCF2129T datasheet(35/73 Pages) NXP

35 / 73 page

PCF2129T

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Product data sheet

Rev. 3 — 12 February 2013

35 of 73

NXP Semiconductors

PCF2129T

Accurate RTC with integrated quartz crystal for industrial

8.11 Timestamp function

The PCF2129T has an active LOW timestamp input pin TS, internally pulled with an

on-chip pull-up resistor to the internal power supply of the device. 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 “AN11186”.

See Section 8.12.5 for a description of interrupt generation from the timestamp function.

8.11.1 Timestamp flag

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

and 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 will clear the interrupt.

Once TSF1 is cleared, it will only be set again when a new negative 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.

c. If the TSIE bit is active, an interrupt on the INT pin is generated.

Fig 18. Timestamp detection with two push-buttons on the TS pin (

for example, for

tamper detection)

116

PCF2129T

215

314

413

512

611

710

push-button 2

connected to

cover 2

push-button 1

connected to

cover 1

VDD

VSS

013aaa568

R1 =

200 kΩ

± 20 %

R2 =

200 kΩ

± 5 %

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