A Matlab/Simulink library for an unsupported microcontroller is developed in this study. The library is implemented by two main steps. First, analyzing and creating Simulink blocks for common peripherals of the microcontroller by using S-Function that combines embedded C language and Target Language Compiler (TLC) language to implement the mechanism for automatic transferring from a peripheral block to a C-embedded program. Second, proposing an algorithm in TLC language to generate automatically an embedded project that links all generated C-files, compile it to binary program, and write to the memory of the target microcontroller. The embedded project is run on the Keil C version 4.0 and the low-cost STM32F4Discovery board developed by STMicroelectronics. The experimental results have shown that the proposed library was designed successfully, generated codes are optimistic, and executed exactly on the target development board. The method in this study can be potentially applied to other microcontrollers.