RCA 1802

The RCA CDP1802, a 40-pin LSI integrated circuit chip (IC), implemented using COSMAC (Complementary Symmetry Monolithic Array Computer) architecture, is an 8-bit CMOS microprocessor (µP) introduced by RCA in early 1976, the company's first single-chip microprocessor. Within RCA in the early days (ca 1970s), the 1801 and 1802 microprocessors were sometimes referred to as "the COSMAC". Hobbyists usually refer to it simply as "the 1802". It is currently^[update] being manufactured by Intersil Corporation as a high-reliability microprocessor. The 1802 has an architecture different from most other 8-bit microprocessors.

In 1970 and 1971, Joseph Weisbecker developed a new 8-bit architecture computer system. RCA released Weisbecker's work as the COSMAC 1801U and 1801R (also known as TA6889/TA6890 and TC 1084/TC 1085) in early 1975, using its CMOS process (called COS/MOS, an acronym for Complementary Silicon/Metal-oxide Semiconductor). In 1976, a team led by Jerry Herzog integrated the two chips into one, the 1802.

Successors to the 1802 are the CDP1804, CDP1805, and CDP1806, which have an extended instruction set, other enhanced features (like on-chip RAM and ROM, and built-in Timer), with some versions running at faster clock speeds, though not a significant speed difference. Some features are also lost, like the DMA auto-boot loader functionality. There are also some minor pin function changes.

The RCA 1802 has a static core CMOS design with no minimum clock frequency, so that it can be run at very low speeds and low power, including a clock frequency of zero to suspend the microprocessor without affecting its operation. It has two separate 8-pin buses: an 8-bit bidirectional data bus and a time-multiplexed address bus, with the high-order and low-order 8-bits of the 16-bit address being accessed on alternate clock cycles.

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