6800

The Motorola MC6800 is an 8-bit microprocessor introduced in 1974. It was one of the early widely adopted CPUs of the 8-bit era and became the cornerstone of Motorola’s 68xx family, which later expanded to include microcontrollers and related peripheral devices. The 6800 offered a balance of performance and simplicity that helped establish its use in early embedded systems and hobbyist microcomputers, competing with Intel's 8080 and Zilog's Z80 during the 1970s.

Architecturally, the 6800 provides an 8-bit data path and a 16-bit address space, allowing access to up to 64 kilobytes of memory. It includes two 8-bit accumulators, A and B, which can be combined to form a 16-bit D register. Additional registers include a 16-bit index register X, a 16-bit program counter PC, and a 16-bit stack pointer SP. Instruction results and status are reported through a condition code register (CCR). The processor supports several addressing modes, including immediate, direct, extended, and indexed, enabling flexible access to memory and I/O. It also uses a two-phase clock and a bus architecture that separates the memory interface from instruction execution, a design choice intended to facilitate peripheral integration.

The 6800 spawned a family of microcontrollers and supporting chips, such as the 6801, 6803, and 6805, which integrated RAM, ROM, and I/O on a single package, and peripheral devices like the 6820 PIA and 6840 PTM. The architecture influenced later CPUs, including Motorola’s own 6809, and contributed to the broader development of early microprocessor-based systems, both in industry and education.