MCP23009 Microchip Technology Inc., MCP23009 Datasheet - Page 14

• Manufacturer Part Number: MCP23009
• Description: 8-bit I/o Expander With Open-drain Outputs
• Manufacturer: Microchip Technology Inc.

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.
© 2008 Microchip Technology Inc.
DS22121A-page 14