Retro Computing: The RCA 1802

Mike Cohen
5 min readDec 15, 2023

My first computer, back in 1978, was a COSMAC Elf, specifically Quest Electronic’s Super Elf, based on RCA’s 1802 CPU.

Quest Super Elf computer

The COSMAC Elf computer was first described in Popular Electronic magazine in 1976. It was a lot simpler and much less expensive than other computers at the time. Several companies, most notably Netronics & Quest Electronics started selling kits and completed systems based on the design.

Quest’s Super Elf was the nicest, with a hex keypad and LED display in a wooden case. It came with a whopping 4K of RAM and bitmapped video output using RCA’s 1861 chip. An optional expansion unit added more memory, a serial interface, a keyboard interface, Tiny Basic in ROM, and an S-100 slot for industry standard cards including video cards.

RCA also had their own 1802-based system, the COSMAC VIP, as well as a video game system. Both used their CHIP-8 interpreter to write games and the 1861 chip for video output.

The 1802 is based on low power CMOS with static RAM that doesn’t require a refresh cycle and only uses a single 5v power supply. This made it much easier and cheaper to design systems with it. It has a built in DMA controller for loading programs via toggle switches (or a hex keypad) without requiring a ROM monitor. It also has a single bit output that can be toggled, which was used to flash an LED or play sounds with a speaker, plus 4 single bit input flags, which can be tested with conditional branch instructions.

The 1802 has 16 general purpose 16-bit registers (GPRs), which was unusual for 8 bit CPUs at the time, although it only has an 8 bit accumulator. Even more unusual, it doesn’t have a dedicated stack pointer or program counter. Instead, you could designate one of the general purpose registers as the program counter or as the index register used for indirect addressing. The first 2 registers are used for DMA & interrupt handling, however.

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Mike Cohen

iOS developer, theater geek, history nerd. Former Bionic Panda. I love San Francisco.