REMOTE 16-BIT I
2
C AND SMBus LOW-POWER I/O EXPANDER
WITH INTERRUPT OUTPUT, RESET, AND CONFIGURATION REGISTERS
SCPS130D – AUGUST 2005 – REVISED MARCH 2007
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DESCRIPTION/ORDERING INFORMATION (CONTINUED)
This 16-bit I/O expander for the two-line bidirectional bus (I
2
C) is designed for 2.3-V to 5.5-V V
CC
operation. It
provides general-purpose remote I/O expansion for most microcontroller families via the I
2
C interface [serial
clock (SCL), serial data (SDA)].
The PCA9539 consists of two 8-bit Configuration (input or output selection), Input Port, Output Port, and Polarity
Inversion (active-high or active-low operation) registers. At power-on, the I/Os are configured as inputs. The
system master can enable the I/Os as either inputs or outputs by writing to the I/O configuration bits. The data
for each input or output is kept in the corresponding Input or Output register. The polarity of the Input Port
register can be inverted with the Polarity Inversion register. All registers can be read by the system master.
The system master can reset the PCA9539 in the event of a timeout or other improper operation by asserting a
low in the RESET input. The power-on reset puts the registers in their default state and initializes the I
2
C/SMBus
state machine. Asserting RESET causes the same reset/initialization to occur without depowering the part.
The PCA9539 open-drain interrupt (INT) output is activated when any input state differs from its corresponding
Input Port register state and is used to indicate to the system master that an input state has changed.
INT can be connected to the interrupt input of a microcontroller. By sending an interrupt signal on this line, the
remote I/O can inform the microcontroller if there is incoming data on its ports without having to communicate via
the I
2
C bus. Thus, the PCA9539 can remain a simple slave device.
The device outputs (latched) have high-current drive capability for directly driving LEDs. The device has low
current consumption.
The PCA9539 is identical to the PCA9555, except for the removal of the internal I/O pullup resistor, which
greatly reduces power consumption when the I/Os are held low, replacement of A2 with RESET, and a different
address range.
Two hardware pins (A0 and A1) are used to program and vary the fixed I
2
C address and allow up to four
devices to share the same I
2
C bus or SMBus.
2
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