This application note presents the clock system configuration tool for the STM32F2xx microcontroller family. The purpose of this tool is to help the user configure the microcontroller clocks, taking into consideration product parameters such as power supply and Flash access mode. The configuration tool supports various functionalities including system clock configuration, HCLK source and output frequency configuration, Flash latency configuration, setting of various frequencies such as PCLK1, PCLK2, TIMCLK (timer clocks), USBCLK, and I2SCLK, and generation of a ready-to-use system_stm32F2xx.c file. It is important to read the STM32F2xx microcontroller reference manual before using the clock tool. This tool supports only revision B and revision Y of the STM32F2xx.