PCF85263AT datasheet(61/100 Pages) NXP

61 / 100 page

PCF85263A

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Product data sheet

Rev. 4.1 — 27 November 2015

61 of 100

NXP Semiconductors

PCF85263A

Tiny RTC with alarm, battery switch-over, and I2C-bus

The stop signal blocks the 8.192 kHz clock from generating system clocks and freezes the

time. In this state, the prescaler can be cleared with the CPR command in the Resets

Remark: The output of clock frequencies is not affected.

The time circuits can then be set and do not increment until the STOP bit is released.

The stop acts on the 8.192 kHz signal. And because the I2C-bus or TS pin input is

asynchronous to the crystal oscillator, the accuracy of restarting the time circuits is

between zero and one 8.192 kHz cycle (see Figure 32).

The first increment of the time circuits is between 0 s and 122

s after STOP is released.

The flow for accurately setting the time in RTC mode is:

• start an I2C access at register 2Eh

• set STOP bit

• send CPR instruction

• address counter rolls over to address 00h

• set time (100th seconds, seconds to years)

• end I2C access

• wait for external time reference to indicate that time counting should start

• start an I2C access at register 2Eh

• clear STOP bit (time starts counting from now)

(1) stop is a combination of STOP register bit and the TS pin when programmed for stop control.

Fig 31. CPR and STOP bit functional diagram

Fig 32. STOP release timing

PCF85263AT Datasheet(PDF) 61 Page - NXP Semiconductors