Datasheet
PCA9554_9554A All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 9 — 19 March 2013 8 of 35
NXP Semiconductors
PCA9554; PCA9554A
8-bit I
2
C-bus and SMBus I/O port with interrupt
6.1.4 Register 2 - Polarity Inversion register
This register allows the user to invert the polarity of the Input Port register data. If a bit in
this register is set (written with ‘1’), the corresponding Input Port data is inverted. If a bit in
this register is cleared (written with a ‘0’), the Input Port data polarity is retained.
6.1.5 Register 3 - Configuration register
This register configures the directions of the I/O pins. If a bit in this register is set, the
corresponding port pin is enabled as an input with high-impedance output driver. If a bit in
this register is cleared, the corresponding port pin is enabled as an output. At reset, the
I/Os are configured as inputs with a weak pull-up to V
DD
.
6.2 Power-on reset
When power is applied to V
DD
, an internal Power-On Reset (POR) holds the
PCA9554/PCA9554A in a reset condition until V
DD
has reached V
POR
. At that point, the
reset condition is released and the PCA9554/PCA9554A registers and state machine will
initialize to their default states. Thereafter, V
DD
must be lowered below 0.2 V to reset the
device.
For a power reset cycle, V
DD
must be lowered below 0.2 V and then restored to the
operating voltage.
Table 7. Register 2 - Polarity Inversion register bit description
Legend: * default value.
Bit Symbol Access Value Description
7 N7 R/W 0* inverts polarity of Input Port register data
0 = Input Port register data retained (default value)
1 = Input Port register data inverted
6N6 R/W 0*
5N5 R/W 0*
4N4 R/W 0*
3N3 R/W 0*
2N2 R/W 0*
1N1 R/W 0*
0N0 R/W 0*
Table 8. Register 3 - Configuration register bit description
Legend: * default value.
Bit Symbol Access Value Description
7 C7 R/W 1* configures the directions of the I/O pins
0 = corresponding port pin enabled as an output
1 = corresponding port pin configured as input
(default value)
6C6 R/W 1*
5C5 R/W 1*
4C4 R/W 1*
3C3 R/W 1*
2C2 R/W 1*
1C1 R/W 1*
0C0 R/W 1*