SC/MP 8-bit Microprocessor Kit

SC/MP Kit Video:

The 1976 National Semiconductor SC/MP microprocessor kit was my first computer! It taught me all about assembly programming and how processor work. I found the kit which I built as a child in my parent's attic, restored it, ran programs I had written in my childhood, and even completed my most ambitious program which I left unfinished 40 years ago.

SC/MP Kit Documentation

The following is a summary of the useful manuals about the SC/MP Kit:

  • The SC/MP Kit Use Manual describes the US version of the board, which has a different format than the European version I have, but is otherwise similar.
  • The Keyboard Kit describes the wire-wrapped calculator keyboard and display interface kit that I added to the basic kit.

SC/MP Kit ROM Listings and Binary Dumps

The kit had two mask 512 Bytes ROMs available:

  • the KITBUG ROM which came with the default kit, and expects a serial interface to a current loop Teletype
  • the SCMPKB ROM which came with the calculator display/keyboard interface add-on

These two ROMs are exclusive, meaning that you either can use the Teletype or the calculator interface depending on which ROM is plugged in.

Below are the commented assembly source listing for reach, as well as the binary dump of the ROMs. In addition, I have created a 1 KB ROM combining both. I used this ROM with my adapter that allowed me to replace my (faulty) mask ROM with a larger Intel 2716 2KB EPROM, and select which of the 512B blocks of firmware to use using switches.

The ROM binary images are provided as 2KB files for programming an Intel 2716 EPROM or equivalent

(Young) CuriousMarc SC/MP Programs

I recovered my hand-assembled programs from my childhood, working freehand on lined paper in the margin of the same pages I had used for some school assignments . I did not have access to another computer, a printer or even less a typewriter. So were the times in 1978, but that sure did not stop me.

The programs were commented well enough that I could still figure out what they did. In retrospect, and considering I learned all by myself from trial and error, they were surprisingly well structured and worked well. A few of them are demonstrated in the video. Below are scans of the programs I retrieved (along with some school assignments), all in French. The English notes were added by me after I recently recovered the listings and tried to make sense of them.

Mask ROM to substitute 2716 EPROM Adapter

I had to improvise a adapter to replace the failed mask ROM chip that originally came with the kit. The original ROM chip is a rather obscure National Semiconductor 512B Mask ROM. Fortunately it had a PROM equivalent, the MM5214, from which I could derive the pinout. It's an old and weird animal, 8x512 bit, requiring +5V and -12V supply, and with a totally non-standard pinout. I made an adapter to replace it with a standard Intel 2716 EPROM, which required some pin shuffling. Since the 2716 is a 8x2048 bit ROM, one can theoretically fit 4 of the original mask ROMS in it. Dip switches are provided to select which 1/4 of the 2716 to use. I created a ROM image to load in the 2716 (see above) which has the two known ROM versions for the kit.

I did not go through the trouble of making a PCB for this adapter, and just wired it on a Jameco PT prototype board.

Datasheets for the ROMs, cross wiring drawing, layout of the board, pictures of the finished board and my lab notes are provided below and should help anyone needing to replicate the adatper.

Case and Power Supply

The kit comes without a case nor a power supply. Inconveniently, it needs +5V and -12V to operate, and the board gets pretty hot with the very inefficient p-MOS chips and a fan is needed in the case.

I used an acrylic case from the Container Store.

The power supply is a SRW-45 4001 from Integrated Power Designs , more pictures and info below.