Shown here is the Nucleo structure. Like the discovery boards, the Nucleo boards also have the ST-LINK built into them, so that that they could be plugged into a PC and it is easy to use a debugger with the devices. There is no external hardware needed. There are two types of extension capability. It has Arduino-compatible connectors on all of the boards, so engineers can reuse Arduino shields on these boards. There is a second set of headers that are compatible across all of the Nucleo boards. These are the Morpho extension headers. All of the STM32 pins are exposed on the Morpho headers, so common extension boards can be built and utilized by designers. The integrated ST-LINK debugger also supports mbed. Mbed is an online development environment that is fully supported with the Nucleo boards. It also supports drag-and-drop flash programming, so users can program the boards without an IDE.