The HT66FB550 is an embedded Flash Microcontroller manufactured by Holtek and packaged in a low-profile quad flat-pack with 48 pins (LQFP-48 RoHS) for surface mount installation on compatible joints or circuit boards. It is based on the Holtek 8-bit HAR supported architecture (HAR80) that uses an 8-bit microprocessor core and advanced internal and on-chip memory options.The device integrates a variety of primary features, including 2K words of embedded Flash program memory, 256-byte RAM data memory, 15 independent I/O ports, four 16-bit general purpose timers, and an ADC. It also provides external interrupt and features for clock input/output, real-time clock, and watchdog timer functions. Moreover, the device includes a Sleep, Power Down, Stop, and Idle mode.It supports two power domains with a voltage range of 2.4V to 5.5V, and provides features for secure operations like Flash-ROM, Anti-Theft, and Code Lock Protection. The device has an operating temperature range of -40 °C to 85 °C. The HT66FB550 is suitable for applications like digital instruments, residential automation, telecom terminals, and consumer electronics.