STM32 cortex ARM nucleo GPIO CubeIDE stm32f 레지스터 저전력 timer backup domain stm32l open drain CubeMX peripheral INTERRUPT 인터럽트 forced toggle on match prescaler rtc 백업 __io_putchar svw bit-banding reigster stm32f429 output compare pinmap ARM Cortex LED밝기 pvd SG90 pullup pulldown open collector PLL ITM assert DWT lsi arr PWM HSI MCU sram 서보모터 register LSE Low power Entry Point 디버깅 음표 HSE standby debug 타이머 Clock sleep 전원 배터리 event Power Frozen stop Memory 스피커 led