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Dawn of a New Computer

In August of 1976 Joseph Weisbecker introduced a new microcomputer to the world in the pages of Popular Electronics magazine. The COSMAC ELF was conceived as a hobbyist computer, as bare-bones as any of the day. The original ELF project featured:

 

  • 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; and
  • One LED connected to the 1802's "Q" output bit.

TinyELF's Emulation of the Classic ELF

Evolution

Several articles appeared in Popular Electronics in the months that followed. In September of 1976 Weisbecker showed readers how to add a hexadecimal keypad to the computer, how to have fun with it's I/O ports and add battery backup to the RAM.

March of 1977 saw Weisbecker's third installment in the series, in which he introduced the concept of an operating system, a "a program that makes it easier to program and use your computer." His ETOPS (Elf Toggle OPerating System) program presented in the article took up 32 bytes of RAM, and EHOPS (Elf Hex OPerating System) consumed a whopping 74 bytes. With only 256 bytes of memory to start with, things were becoming a little tight, so Weisbecker went on to describe the construction of a 1,024 byte memory expansion.

Weisbecker's Starship Running on TinyELFIn July of 1977 Weisbecker added graphics to the ELF using RCA's 1861 "PIXIE" graphics chip. This odd little beast had a resolution of 64 bits wide by 128 bits high, and interfaced to the 1802 by its interrupt line, one of the 1802's four "external flag" input lines, and the 1802's version of DMA. Programming for the 1861 was tricky, requiring careful timing and cycle counting in the interrupt service routine. By manipulating the DMA pointer, software could create the appearance of lower vertical resolutions. Weisbecker published an example of a 64x32 display featuring a starship image which would forever be associated with the ELF computers.

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