Datasheet

MCP23009/MCP23S09

1.5 GPIO Port

The GPIO module is a general purpose 8-bit wide

bidirectional port.

The outputs are open-drain.

The GPIO module contains the data ports (GPIOn),

internal pull up resistors and the Output Latches

(OLATn).

The pull up resistors are individually configured and

can be enabled when the pin is configured as an input

or output.

Reading the GPIOn register reads the value on the

port. Reading the OLATn register only reads the

latches, not the actual value on the port.

Writing to the GPIOn register actually causes a write to

the latches (OLATn). Writing to the OLATn register

forces the associated output drivers to drive to the level

in OLATn. Pins configured as inputs turn off the

associated output driver and put it in high-impedance.