PCA88021 datasheet(5/34 Pages) NXP

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PCA8802_1

Product data sheet

Rev. 01 — 19 February 2009

5 of 34

NXP Semiconductors

PCA8802

Smartcard RTC

Functional description

The PCA8802 is an ultra low power device for battery operations. The integrated oscillator

circuit generates a 1

⁄

32 Hz clock signal to increment a 24 bit counter. The communication

between the PCA8802 and other devices is made via an I2C-bus.

The device is always running but for longer storage time it can be switched off and on

again in case of delivery.

The functions of the device can be controlled with the following instruction set:

9.1 Oscillator

The 32.768 kHz oscillator includes two integrated load capacitors and an automatic gain

control to ensure a reliable start-up.

For prototype development and system debugging, it is possible to output a 32.768 kHz

square wave on the INT pin with the 32k_cmd instruction.

9.1.1 Power-on

At initial power-on, when the oscillator has not yet started, a reset will be generated.

During this state the serial interface will not respond when accessed. To ensure that the

oscillator has started and the serial interface is accessible, it is recommended that the

master attempts to make write-read accesses to the counter register.

Table 4.

Instruction set overview

Instruction

Description

Reference

wrt_cmd

device write access

Section 9.6.2

dvs_cmd

divider start or stop switch

Section 9.6.3

pwd_cmd

low power mode switch

Section 9.6.4

32k_cmd

32.768 kHz clock signal on the pin INT switch

Section 9.6.5

fst_cmd

fast system development mode switch

Section 9.6.6

set_cmd

set counter instruction

Section 9.6.7

rd_cmd

counter read instruction

Section 9.6.8

Exit from Power-down mode will give the same behavior as start-up.

Fig 5.

Power-on reset

001aaj166

oscillation now stable

oscillation

instructions will be ignored

VDD

instructions will be accepted

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