STARTUP.A51 is the MCU initialization routine included in the KEIL compiler. It is executed before main() and initializes RAM etc.
Modification may be required depending on the MCU used. For MCUs with a large RAM size, the Watchdog timer may cause a reset during initialization, so the Watchdog timer must be disabled in advance. Also, in the case of an MCU with USB, the USB clock is used to initialize the RAM, so it is necessary to set the clock in advance. Therefore, it is necessary to modify STARTUP.A51.
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