PCA9538 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2017. All rights reserved.
Product data sheet Rev. 8 — 8 November 2017 8 of 34
NXP Semiconductors
PCA9538
8-bit I
2
C-bus and SMBus low power I/O port with interrupt and reset
6.2.5 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.
6.3 Power-on reset
When power is applied to V
DD
, an internal Power-On Reset (POR) holds the PCA9538 in
a reset condition until V
DD
has reached V
POR
. At that point, the reset condition is released
and the PCA9538 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.
6.4 RESET input
A reset can be accomplished by holding the RESET pin LOW for a minimum of t
w(rst)
.
The PCA9538 registers and SMBus/I
2
C-bus state machine will be held in their default
state until the RESET
input is once again HIGH. This input requires a pull-up resistor to
V
DD
if no active connection is used.
6.5 Interrupt output
The open-drain interrupt output (INT) is activated when one of the port pins changes state
and the pin is configured as an input. The interrupt is de-activated when the input returns
to its previous state or the Input Port register is read.
Note that changing an I/O from an 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.
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 an 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*
