I made a RCA SuperElf, by Tom
1977. I read the article in Popular
Electronics (later Eletronics, Now!) and etched the board, bought chips,
soldered and populated. I taught myself binary, hex and machine language
with the hex keypad, load, save, run and single step push buttons, 256
bytes (!) of memory and dual 7-segment displays.
I believe I spent $250-300 in this effort as well as hundreds of
hours. I remember that since the RCA1802 processor was CMOS I could run
the thing off of a battery for days at a time. The board I etched was from
the P.E. plans so it had 3-4 "card slots". I bought (mail order)
2 x 4K RAM cards for $80 apiece and a "Super IO card" for
another $40(?) that held 2 RS-232 serial ports as well as two
toggle pins direct from the processor that were used for input and output
to two cassette decks (8" floppies were available but were over $1000
I accquired an ADM3A Lear-Siegler dumb terminal ($400) and an
Integral Data Systems Paper Tiger printer ($400) to make it a real
computer. So by the time I was done, I had spent about $1250 for
this 8.25KB machine. Oh, I almost forgot the $300 1200baud
There was a Canadian-based (Ontario) fan-club (COSMAC, I think) that
published a newsletter in which many of us published our programs. I wrote
one that was a simple screen typewriter (it used self-modifying code to
circumvent the small memory space). Someone else wrote one called
"Indigenous Music" that cycled bits back and forth through the
registers of the processor and then spit them out the CD4 pin of the 1802
attached to a speaker. Seemed like the computer was making up its own
music. I learned a lot from that machine that I carry with me to this day..
About the Q line, by Richard
In your description of the Super Elf you
write that sound was produced by software over the Q line.
This is true, but the Q line had some more important functions. It was the
only I/O line available which could be controlled by the CPU directly.
Therefore it was used primarily to generate the signal for recording
programs to tape as well. Often serial terminals were connected to an Elf
(both Netronics and Quest had terminal kits) and the Q line served in a
triple function as RS232 C serial interface, again driven by software.
Usually there were additional switches to mut the speaker or to cut off
the data to the terminal since you did not want garbage on your terminal's
screen while saving a program or playing sound. Also you would not want to
hear the data going to the tape recorder or the terminal. And using more
than one of these at once was not possible.
Again all this is for a typical Elf, but modifications to solve these
problems were possible at the price of sacrificing compatibility.