The NuMicro MS51 series is an embedded Flash-type, 8-bit high-performance 1T 8051 microcontroller. Its instruction set is fully compatible with the standard 80C51, and its performance has been enhanced. The MS51 series includes up to 32 Kbytes of main Flash, called APROM, where user code is stored. The Flash supports In-Application Programming (IAP) functionality, which enables on-chip firmware updates. IAP also allows any block in the user code array to be configured as non-volatile data storage, which can be written via IAP and read by IAP or the MOVC instruction. In addition, there is a Flash called LDROM, which is typically used to store boot code executed during In-System Programming (ISP). The size of the LDROM is configurable, up to a maximum of 4 Kbytes. For ease of programming and verification, the Flash can be electronically programmed and read via a parallel writer or In-Circuit Programming (ICP). Once the code is verified, users can lock the code to ensure security. The MS51 series provides a rich set of peripherals, including 256 bytes of SRAM, up to 2 Kbytes of auxiliary RAM (XRAM), up to 30 general-purpose I/Os, two 16-bit timers/counters 0/1, a 16-bit timer 2 with a three-channel input capture module, a watchdog timer (WDT), a wake-up timer (WKT), a 16-bit auto-reload timer 3 for general-purpose or baud rate generation, two UARTs with frame error detection and auto-address recognition features, an SPI, an I2C, up to 12 enhanced PWM output channels, and a 12-bit ADC. The peripherals are equipped with 18 interrupt sources, supporting 4-level priority interrupts. The MS51 series is equipped with two clock sources and supports real-time switching via software. The clock sources include an internal clock input, a 10 kHz internal oscillator, and a 24 MHz internal precise oscillator, which is factory-calibrated to ±1% at room temperature. The MS51 series also provides additional power monitoring detection functions, such as power-on reset and 4-level power-down detection, which help stabilize the system's power-on/power-off sequence, thereby designing highly reliable systems. The MS51 series microcontrollers have very low power consumption, providing two economical power modes to reduce power consumption—idle mode and power-down mode, which can be selected via software. Idle mode turns off the CPU clock but allows peripheral operations to continue. Power-down mode stops the entire system clock to achieve the lowest power consumption. The system clock of the MS51 series can also be slowed down via a software clock divider, providing flexibility between execution performance and power consumption.