A user interface for a building appliance controller that may include a control panel and one or more option cards. The user interface may allow a user or technician to program, modify, and/or view one or more parameters of the control panel and/or the one or more option cards. In some cases, the control panel may be configured to send one or more messages to a selected option card that indicate an input at the user interface, and in response, the selected option card may send one or more messages to the control panel that indicate display information for display on the user interface of the control panel. In some embodiments, such as when the user interface includes a segmented display, the display information may include the on/off state of the various segments of the display.