PCA9554_9554A_7

© NXP B.V. 2006. All rights reserved.

Product data sheet

Rev. 07 — 13 November 2006

9 of 30

NXP Semiconductors

PCA9554/PCA9554A

6.3 Interrupt output

The open-drain interrupt output is activated when one of the port pins change state and

the pin is configured as an input. The interrupt is deactivated when the input returns to its

previous state or the Input Port register is read.

Note that changing an I/O from and output to an input may cause a false interrupt to occur

if the state of the pin does not match the contents of the Input Port register.

6.4 I/O port

When an I/O is configured as an input, FETs Q1 and Q2 are off, creating a

high-impedance input with a weak pull-up (100 k

Ω typ.) to V

If the I/O is configured as an output, then either Q1 or Q2 is enabled, depending on the

state of the Output Port register. Care should be exercised if an external voltage is applied

to an I/O configured as an output because of the low-impedance paths that exist between

Remark: At power-on reset, all registers return to default values.

Fig 9.

Simplified schematic of IO0 to IO7

IO0 to IO7

output port

register data

configuration

register

DQ

CK

Q

data from

shift register

write configuration

pulse

output port

register

DQ

CK

write pulse

polarity inversion

register

DQ

CK

data from

shift register

write polarity

pulse

input port

register

DQ

CK

read pulse

input port

register data

polarity inversion

register data

002aac493

FF

data from

shift register

FF

FF

FF

Q1

Q2

to INT

100 k

Ω