PCF2131 datasheet(5/85 Pages) NXP

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NXP Semiconductors

PCF2131

Nano-power highly accurate RTC with integrated quartz crystal

Input or input/output pins must always be at a defined level (VSS or VDD) unless otherwise specified.

Symbol

Description

VBAT

battery supply voltage (backup)

connect to VSS if battery switch-over is not used

VDD

supply voltage

Exposed Pad

Tie to VSS (preferred)[1] or leave floating

Table 3. Pin description...continued

[1]

This protects against signal feedback to the oscillator if routed close to the part.

7 Functional description

The PCF2131 is a Real Time Clock (RTC) and calendar with an on-chip Temperature Compensated Crystal

(Xtal) Oscillator (TCXO) and a 32.768 kHz quartz crystal integrated into the same package.

Address and data are transferred by a selectable 400 kHz Fast-mode I2C-bus or a 4-line SPI-bus with separate

data input and output (see Section 7.16). The maximum speed of the SPI-bus is 6.5 Mbit/s.

The PCF2131 has a backup battery input pin and backup battery switch-over circuit which monitors the main

power supply. The backup battery switch-over circuit automatically switches to the backup battery when a power

failure condition is detected (see Section 7.5.1). Accurate timekeeping is maintained even when the main power

supply is interrupted.

A battery low detection circuit monitors the status of the battery (see Section 7.5.2). When the battery voltage

drops below a certain threshold value, a flag is set to indicate that the battery must be replaced soon. This

ensures the integrity of the data during periods of battery backup.

7.1 Register overview

The PCF2131 contains an auto-incrementing address register: the built-in address register will increment

automatically after each read or write of a data byte up to the register 36h. After register 36h, the auto-

incrementing will wrap around to address 00h (see Figure 3).

aaa-041564

address register

00h

auto-increment

wrap around

01h

02h

03h

...

34h

35h

36h

Figure 3. Handling address registers

• The first five registers (memory address 00h, 01h, 02h, 03h and 04h) are used as control registers (see

Section 7.2).

• The register at address 05h is for software reset.

• The memory addresses 06h through to 0Dh are used as counters for the clock function (1/100 seconds

up to years). The date is automatically adjusted for months with fewer than 31 days, including corrections

for leap years. The clock can operate in 12-hour mode with an AM/PM indication or in 24-hour mode (see

Section 7.9).

PCF2131

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

Product data sheet

Rev. 2.0 — 5 October 2023

5 / 85

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