Equipments used in industrial field require downtime for firmware updates when functions are added, changed, or for maintenance. Various methods to reduce downtime are studied, especially in high-availability systems such as server power supplies or measurement applications for continuous monitoring. One of the methods is making system redundancy, however, a method for real-time software update is required due to cost issues. For real-time software update, an MCU with a dual flash memory structure that supports the LFU function can be used, but high-performance MCUs have a single flash memory structure, so the update method through a dual flash memory structure cannot be used. In this study, the firmware executable file is converted to hex format and directly compared with data loaded into flash memory. The method in which the firmware can be run even if the flash memory is initialized is proposed and confirmed the applicability of LFU in high-performance MCUs with a single flash structure.