The Cosmac “Elf”

The Cosmac “Elf”

In August 1976 issue of Popular Electronics magazine, Joseph Weisbecker published a design for “Low-cost experimenter’s microcomputer” using RCA’s COSMAC CDP1802 microprocessor chip. It is a very simple computer having 256 bytes of memory, switches as input and LED as output. No ROM, every time you turn it on you have to enter program to RAM by toggling 8 switches, one for each bit. After the switches are set, pressing IN-button stores that byte to memory and increments address. Remember, that it only had 256 bytes of RAM, so it was not that big deal, but still takes some time. There is no way to step address backwards – if you made a mistake you have to start from beginning. COSMAC ELF became a hit among hobbyists in the USA.

It was simple to build by almost anyone and the components didn’t cost much. Later more designs based on ELF like Netronics ELF II and Quest Super-ELF appeared.





RCA’s eight-bit “COSMAC” CDP-1802 microprocessor
256 bytes of static RAM
Eight toggle switches and a pushbutton for data input
Two toggle switches to control the CPU’s mode
One toggle switch to control write access to the memory
A two-character hexadecimal display
One LED connected to the 1802’s “Q” output bit.


Here is my Cosmac Elf.


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