PCA88021 datasheet(8/34 Pages) NXP

8 / 34 page

PCA8802_1

Product data sheet

Rev. 01 — 19 February 2009

8 of 34

NXP Semiconductors

PCA8802

Smartcard RTC

9.4 Pulse generator

An interrupt pulse is available at the INT pin. This pulse is generated once every

32 seconds and could be used to wake up a microcontroller to perform a periodic function

e.g. to calculate and update an LCD display with a new one-time password.

A pulse is generated coincident with the increment of the counter. The new counter value

will be available immediately.

9.5 I2C-bus interface

9.5.1 Interface protocol

The serial interface is based on the I2C-bus protocol. The I2C-bus protocol has the

advantage of being robust in terms of immunity to electrical noise. Although the PCA8802

does not have the signal ﬁlters inside the interface pins, the slave address and

acknowledge hand shaking is nevertheless implemented.

For power saving, the SDA output is push-pull instead of the more traditional open-drain

output. Push-pull prevents the need for power consuming pull-up resistors, but does limit

the operation to point to point only.

The following slave addresses plus a write and read bit are reserved for the PCA8802:

• write: 1010 0000

• read: 1010 0001

An incorrect slave address will result in the device ignoring all bus data. A STOP or

START condition (see Section 9.5.4) will be required before a new transfer can be made.

9.5.1.1

The writing protocol

The writing protocol is shown in Figure 10.

There is no restriction for the order of sending instructions. As many instructions as

needed may be sent in one access. The total duration of one access must not exceed

32 seconds (see Figure 12).

Fig 9.

Pulse generator

001aaj169

INT

counter

PCA88021 Datasheet(PDF) 8 Page - NXP Semiconductors