From here:
http://en.wikipedia.org/wiki/COSMAC_ELF you can find the datasheets etc. in the external links.
I may have not used the ELF, but I think I did. the way the system worked was you had a programming board and a processor board. The programming board had a LED display and Keypad and ways to dingle-step the program. There was a programming option, so you could take away the programming board and the processor board would run by itself.
I had trouble, or didn't wait long enough to download the user's manual. Long .pdf files won't load directly with an embedded browser link with my computer/software. Acrobat 9 chokes when you touch the page before it's done loading.