This 8-bit I/O expander for the two-line bidirectional bus
(I2C) is designed for 2.3-V to 5.5-V VCC
operation. The device provides general-purpose remote I/O expansion for most microcontroller
families via the I2C interface [serial clock (SCL) and serial data
The PCA9557 consists of one 8-bit configuration (input or output selection), input port,
output port, and polarity inversion (active-high) registers. At power on, the I/Os are configured
as inputs. However, 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 device outputs (latched) have high-current drive capability for directly driving
LEDs. The device has low current consumption.
The system master can reset the PCA9557 in the event of a timeout or other improper
operation by asserting a low in the active-low reset (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 depowering the part.
Three hardware pins (A0, A1, and A2) are used to program and vary the fixed
I2C address, allowing up to eight devices to share the same
I2C bus or SMBus.