PCA9675DB datasheet(12/34 Pages) PHILIPS

12 / 34 page

PCA9675_1

Product data sheet

Rev. 01 — 1 February 2007

12 of 34

NXP Semiconductors

PCA9675

Remote 16-bit I/O expander for Fm+ I2C-bus with interrupt

I/O programming

8.1 Quasi-bidirectional I/O architecture

The PCA9675’s 16 ports (see Figure 2) are entirely independent and can be used either

as input or output ports. Input data is transferred from the ports to the microcontroller in

the Read mode (see Figure 17). Output data is transmitted to the ports in the Write mode

(see Figure 16).

Every data transmission from the PCA9675 must consist of an even number of bytes, the

ﬁrst byte will be referred to as P07 to P00, and the second byte as P17 to P10. The third

will be referred to as P07 to P00, and so on.

This quasi-bidirectional I/O can be used as an input or output without the use of a control

signal for data directions. At power-on the I/Os are HIGH. In this mode only a current

source (IOH) to VDD is active. An additional strong pull-up to VDD (Itrt(pu)) allows fast rising

edges into heavily loaded outputs. These devices turn on when an output is written HIGH,

and are switched off by the negative edge of SCL. The I/Os should be HIGH before being

used as inputs. After power-on, as all the I/Os are set HIGH, all of them can be used as

inputs. Any change in setting of the I/Os as either inputs or outputs can be done with the

write mode.

Remark: If a HIGH is applied to an I/O which has been written earlier to LOW, a large

current (IOL) will ﬂow to VSS.

8.2 Writing to the port (Output mode)

To write, the master (microcontroller) ﬁrst addresses the slave device. By setting the last

bit of the byte containing the slave address to logic 0 the Write mode is entered. The

PCA9675 acknowledges and the master sends the ﬁrst data byte for P07 to P00. After the

ﬁrst data byte is acknowledged by the PCA9675, the second data byte P17 to P10 is sent

by the master. Once again, the PCA9675 acknowledges the receipt of the data. Each 8-bit

data is presented on the port lines after it has been acknowledged by the PCA9675.

The number of data bytes that can be sent successively is not limited. After every two

bytes, the previous data is overwritten.

The ﬁrst data byte in every pair refers to Port 0 (P07 to P00), whereas the second data

byte in every pair refers to Port 1 (P17 to P10). See Figure 15.

Fig 15. Correlation between bits and ports

002aab634

first byte

P06 P05 P04 P03 P02 P01 P00

P07

second byte

P16 P15 P14 P13 P12 P11 P10

P17

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