Mikroe MCU CARD 13 for STM32 STM32L151ZD allows for installation and replacement of the microcontroller unit (MCU) on a development board. The new MCU Card standard ensures compatibility between the development board and any of the supported MCUs, regardless of their pin number and compatibility. MCU Cards are equipped with two 168-pin mezzanine connectors, allowing them to support even MCUs with extremely high pin count. The clever design allows for usage with the plug & play concept of the Click board™ line.