Totem-pole devices require that the users program the Port Configuration Register when switching a pin between input and output. Totem-pole devices also have other configuration registers to control the I/O. One of these features is the Configuration Port Register, which defines the direction of each I/O pin. Next is the Input Port Register. This reflects the incoming logic level of the pins, irrespective of pin definition in the Configuration Port Register. The Output Port Register reflects the outgoing logic levels of the pins defined as outputs in the Configuration Port Register. Additionally, the user can invert the polarity of the Input Port Register data by setting bits in the Polarity Inversion Port Register. Some I/O expanders have Bus-Hold, Resistor Pull-Up or Pull-Down Enable, and Selector Port Registers which allow the user to enable or disable the bus-hold, pull-up or pull-down on the I/O pins. Finally, the Interrupt Status Port Register identifies the source of an interrupt while the Interrupt Mask Port Register enables or disables the interrupt for an individual pin.