This 16-bit I/O expander for the two-line bidirectional bus
(I2C) is designed for 2.3-V to 5.5-V VCC
operation. It provides general-purpose remote I/O expansion for most microcontroller families via
the I2C 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 time-out 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 I2C/SMBus state
machine. Asserting RESET causes the same reset/initialization to occur
without de-powering 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 I2C
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
I2C address and allow up to four devices to share the same
I2C bus or SMBus.