MC6805

The MC6805 is an 8-bit microcontroller family developed by Motorola (now Freescale/NXP) for embedded control applications. Introduced in the late 1970s, the MC6805 combines a CPU core with on‑chip RAM and input/output peripherals, enabling compact, low‑cost control devices without requiring large external memories.

Architecturally, the MC6805 implements an 8‑bit data path and a modest register set, including an accumulator, a program counter, a stack pointer, and a condition code register. It executes a compact instruction set derived from the 6800 family and supports multiple addressing modes, including direct and indirect. Interrupts are supported, and programs are typically stored in external ROM while data memory is addressed in the same space or through on‑chip RAM on certain variants.

Peripheral integration and variants vary within the family. Many MC6805 devices include on‑chip RAM and I/O ports, and some models integrate timers or serial interfaces. Depending on the variant, program memory and RAM sizes differ, with options for external ROM or RAM for larger applications. The devices were commonly offered in DIP packages and other form factors suitable for embedded systems.

Impact and legacy: The MC6805 family were widely used in automotive electronics, consumer appliances, and instrumentation during the 1980s. They formed the basis for later Motorola 8‑bit lines, notably the 68HC05 family, and influenced subsequent microcontroller designs that integrated CPU, memory, and peripherals on a single chip.