Les Lab | Cosmac Elf @LesLaboratory | Uploaded 8 years ago | Updated 1 hour ago
This machine is based on the 1976 article from Popular Electronics.
It is an 8-bit micro using a CDP1802 CPU with a whopping 256 bytes of RAM.
Programming is done using the 8 toggle switches on the main panel to toggle in the bytes!
Although I have built the main panel following the original specification in the article, I have made several enhancements to the original design, although all additional components used for them were available in the 70's
Enhancements include:
Clock modification as per later articles in Popular electronics, i.e. a 3.579 MHz crystal divided by two for the main clock.
The addition of an address display (top right, main panel)
Hexadecimal keypad with display on the right, as well as a slow clock (down to 2Hz) to watch running programs step through memory, and a speaker connected via a transistor to the Q line.
On the left is a CDP1864 display chip. I couldn't source a CDP1861, but did manage to get the PAL equivalent! So I can do video.
The circuit is modified to include a 'front porch' generator since modern monitors seem to balk at simple video signals.
Also on the left is a cool eprom reader of my own design with address LED's (bottom row) and data (top row).
It is simply a clock, connected to a binary ripple counter which drives the address bus.
The clock itself is divided by a flipflop, the Q pulse drives the ripple counter, i.e does a read, and !Q provides a pulse to tell the ELF to write the data to RAM.
This video demonstrates loading in the 256 byte program found in Popular electronics that displays video. There is no logic yet to stop loading at address FF, so the clock is stopped short, and the remaining bytes clocked in manually.
This machine is based on the 1976 article from Popular Electronics.
It is an 8-bit micro using a CDP1802 CPU with a whopping 256 bytes of RAM.
Programming is done using the 8 toggle switches on the main panel to toggle in the bytes!
Although I have built the main panel following the original specification in the article, I have made several enhancements to the original design, although all additional components used for them were available in the 70's
Enhancements include:
Clock modification as per later articles in Popular electronics, i.e. a 3.579 MHz crystal divided by two for the main clock.
The addition of an address display (top right, main panel)
Hexadecimal keypad with display on the right, as well as a slow clock (down to 2Hz) to watch running programs step through memory, and a speaker connected via a transistor to the Q line.
On the left is a CDP1864 display chip. I couldn't source a CDP1861, but did manage to get the PAL equivalent! So I can do video.
The circuit is modified to include a 'front porch' generator since modern monitors seem to balk at simple video signals.
Also on the left is a cool eprom reader of my own design with address LED's (bottom row) and data (top row).
It is simply a clock, connected to a binary ripple counter which drives the address bus.
The clock itself is divided by a flipflop, the Q pulse drives the ripple counter, i.e does a read, and !Q provides a pulse to tell the ELF to write the data to RAM.
This video demonstrates loading in the 256 byte program found in Popular electronics that displays video. There is no logic yet to stop loading at address FF, so the clock is stopped short, and the remaining bytes clocked in manually.
