PCA8574_PCA8574A_2

© NXP B.V. 2007. All rights reserved.

Product data sheet

Rev. 02 — 14 May 2007

12 of 27

NXP Semiconductors

PCA8574/74A

10. Application design-in information

10.1 Bidirectional I/O expander applications

In the 8-bit I/O expander application shown in Figure 15, P0 and P1 are inputs, and P2 to

P7 are outputs. When used in this configuration, during a write, the input (P0 and P1)

must be written as HIGH so the external devices fully control the input ports. The desired

HIGH or LOW logic levels may be written to the I/Os used as outputs (P2 to P7). During a

read, the logic levels of the external devices driving the input ports (P0 and P1) and the

previous written logic level to the output ports (P2 to P7) will be read.

The GPIO also has an interrupt line (INT) that can be connected to the interrupt logic of

the microprocessor. By sending an interrupt signal on this line, the remote I/O informs the

microprocessor that there is incoming data or a change of data on its ports without having

10.2 High current-drive load applications

The GPIO has a maximum sinking current of 25 mA per bit. In applications requiring

additional drive, two port pins in the same octal may be connected together to sink up to

50 mA current. Both bits must then always be turned on or off together. Up to 8 pins (one

octal) can be connected together to drive 200 mA.

Fig 15. Bidirectional I/O expander application

002aac123

temperature sensor

battery status

control for latch

control for switch

control for audio

control for camera

control for MP3

P0

P1

P2

P3

P4

P5

P6

P7

SDA

SCL

INT

AD0

AD1

AD2

CORE

PROCESSOR

Fig 16. High current-drive load application

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P0

P1

P2

P3

P4

P5

P6

P7

SDA

SCL

INT

AD0

AD1

AD2

CORE

PROCESSOR

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