The 68HC05 (HC05 in short) is a broad family of 8-bit microcontrollers from Freescale Semiconductor (formerly Motorola Semiconductor).
Like all Motorola processors that share lineage from the 6800, they use the von Neumann architecture as well as memory-mapped I/O. This family has five CPU registers that are not part of the memory. One 8-bit accumulator A, a 8-bit index register X, a 8-bit stack pointer SP with two most significant bits hardwired to 1, a 13-bit program counter PC, and an 8-bit condition code register CCR.
Among the HC05's there are several processor families, each targeted to different embedded applications.
The HC05 series is now considered legacy and is replaced by the HC(S)08 MCU series.