1.0 DEVICE OVERVIEW
The MCP23X09 device provides 8-bit, general purpose
parallel I/O expansion for I2C bus or SPI applications.
The two devices differ only in the serial interface.
• MCP23009 – I2C interface
• MCP23S09 – SPI interface
The MCP23X09 consists of multiple 8-bit configuration
registers for input, output and polarity selection. The
system master can enable the I/Os as either inputs or
outputs by writing 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 interrupt output can be configured to activate
under two conditions (mutually exclusive):
1. When any input state differs from its
corresponding input port register state. This is
used to indicate to the system master that an
input state has changed.
2. When an input state differs from a
pre-configured register value (DEFVAL
The Interrupt Capture register captures port values at
the time of the Interrupt, thereby saving the condition
that caused the Interrupt.
The Power-On Reset (POR) sets the registers to their
default values and initializes the device state machine.
The hardware address pin is used to determine the
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