What version of OH do you have? In 2.3 there is a problem with MCP23017 binding but here you have workaround Problem with new MCP23017 binding in Openhab 2.3
I use this binding https://www.openhab.org/addons/bindings/mcp23017/#supported-things
What version of OH do you have? In 2.3 there is a problem with MCP23017 binding but here you have workaround Problem with new MCP23017 binding in Openhab 2.3
I use this binding https://www.openhab.org/addons/bindings/mcp23017/#supported-things