1. General description
The PCA9501 is an 8-bit I/O expander with an on-board 2-kbit EEPROM.
The I/O expandable eight quasi-bidirectional data pins can be independently assigned as
inputs or outputs to monitor board level status or activate indicator devices such as LEDs.
The system master writes to the I/O configuration bits in the same way as for the
PCF8574. The data for each input or output is kept in the corresponding input or output
register. The system master can read all registers.
The EEPROM can be used to store error codes or board manufacturing data for
read-back by application software for diagnostic purposes and are included in the I/O
expander package.
The PCA9501 active LOW open-drain interrupt output is activated when any input state
differs from its corresponding input port register state. It is used to indicate to the system
master that an input state has changed and the device needs to be interrogated.
The PCA9501 has six address pins with internal pull-up resistors allowing up to
64 devices to share the common two-wire I
2
C-bus software protocol serial data bus. The
fixed GPIO address starts with ‘0’ and the fixed EEPROM I
2
C-bus address starts with ‘1’,
so the PCA9501 appears as two separate devices to the bus master.
The PCA9501 supports hot insertion to facilitate usage in removable cards on backplane
systems.
2. Features
n 8 general purpose input/output expander/collector
n Replacement for PCF8574 with integrated 2-kbit EEPROM
n Internal 256 × 8 EEPROM
n Self timed write cycle (5 ms typical)
n 16 byte page write operation
n I
2
C-bus and SMBus interface logic
n Internal power-on reset
n Noise filter on SCL/SDA inputs
n Active LOW interrupt output
n 6 address pins allowing up to 64 devices on the I
2
C-bus/SMBus
n No glitch on power-up
n Supports hot insertion
n Power-up with all channels configured as inputs
PCA9501
8-bit I
2
C-bus and SMBus I/O port with interrupt, 2-kbit
EEPROM and 6 address pins
Rev. 04 — 10 February 2009 Product data sheet
