Integrated Circuit


MCP23017/MCP23S17 16-Bit I/O Expander with Serial Interface (I2C/SPI)

The MCP23017/MCP23S17 (MCP23X17) device
family provides 16-bit, general purpose parallel I/O
expansion for I2C bus or SPI applications. The two
devices differ only in the serial interface.
• MCP23017 – I2C interface
• MCP23S17 – SPI interface
The MCP23X17 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 (IODIRA/B).
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 16-bit I/O port functionally consists of two 8-bit
ports (PORTA and PORTB). The MCP23X17 can be
configured to operate in the 8-bit or 16-bit modes via

There are two interrupt pins, INTA and INTB, that can
be associated with their respective ports, or can be
logically OR’ed together so that both pins will activate if
either port causes an interrupt.
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 preconfigured
register value (DEFVAL register).
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 pins are used to determine the
device address.




  1. MCP23017/MCP23S17 16-Bit I/O Expander with Serial Interface (I2C/SPI)