Looking closer at the modules that comprise a Tower System, there are three types of boards, or modules: the MCU/MPU modules, peripheral modules, and the Elevator modules. The MCU/MPU module serves as the main control board and the basic building block of the NXP Tower System. Each MCU module includes Open Source BDM debug hardware, allowing it to become a standalone BDM tool. In any given Tower System configuration, the MCU module is the single control module. Peripheral modules provide added features and functionality, like Serial, Ethernet, RS232/485 and CAN connectivity, to the development platform. They are designed to be connected to and used with other microcontroller and peripheral modules in the Tower System. There can be up to three peripheral modules in an assembled Tower System. The Functional and Dummy Elevator modules are the central connection point in the NXP Tower System. Sold in sets of two, the elevator modules are designed to connect microcontroller and peripheral modules.