The SB-593 Satellite Expansion Board plugs into the PXL-500 to provide additional functionality at a cost far less than that of adding another controller. The SB-593 gives each PXL-500 an additional 8 general purpose inputs and 4 general purpose outputs. Two of the inputs and outputs can be con gured to manage a second door, making the PXL-500 a cost e ective two door controller while still providing an additional 6 inputs and 2 outputs.