6559

The 6559 is a 16-bit central processing unit (CPU) designed by the American semiconductor company RCA Corporation in the late 1970s. It was part of RCA’s COSMAC microcomputer series, which aimed to compete with other early microprocessors like the Intel 8080 and Motorola 6800. The 6559 was notable for its unique architecture, which combined a CPU with a programmable peripheral interface (PPI) and a timer, all integrated into a single chip.

Unlike many contemporary microprocessors, the 6559 featured a Harvard architecture, separating its instruction and data buses. This design allowed for faster execution of certain operations, particularly those involving memory access. The chip operated at a clock speed of 1 MHz and included 16 bits of internal data bus width, enabling it to address up to 64 kilobytes of memory. Its instruction set was relatively simple, with around 50 commands, but it was optimized for efficiency in embedded and control applications.

The 6559 was primarily used in educational and hobbyist microcomputer systems, such as the RCA COSMAC ELF and the later COSMAC VIP. It also found applications in industrial control systems and early home computing devices. Despite its technical merits, the 6559 did not achieve widespread commercial success, partly due to RCA’s declining influence in the semiconductor market during the 1980s. Today, the chip is of historical interest to retro computing enthusiasts and is occasionally used in vintage computer restorations.

The 6559’s legacy lies in its innovative design and its role in expanding the capabilities of early microprocessors. While it did not dominate the market, it contributed to the evolution of microcontroller technology, influencing later integrated solutions that combined processing and peripheral control.