MMD-1

E&L MMD-1 Mini-Micro Designer

The E&L MMD-1 is a micro-computer trainer designed by Jon Titus and published in 1976 in Radio Electronics. It was sold fully assembled or as a kit by E&L, who had a large offering of breadboard systems.  It has an Intel 8080 processor, 512 bytes of ROM and 51 bytes of RAM, a row of 24 LEDs, a simple keyboard, and last but not least, a breadboard area. The breadboard has some of its pins connected to the important data bus, memory bus and control signals. It's a cute and cleverly designed minimal viable system to learn the 8080 processor. and arguably the first single board microprocessor system.

The design was originally published in the May 1976 edition of Radio Electronics, and called the Dyna Micro.

The design in the brainchild of Jon Titus, who is probably better known for his previous Mark  8 design, built around the earlier 8008 processor, one of the very first personal microcomputers. The Mark 8 was also published in Radio Electronics.  We interview Jon Titus and his partner in crime David Larsen (from the Blacksburg computing group) in one of the videos.

The MMD-1 was meant as the hardware companion to the Bugbooks V and VI series. The books, written by David Larsen, Jon Titus and Peter Rony, are still copyright protected and pretty hard to find on eBay. They are aimed at complete beginners and are therefore basic, slow and detailed in their explanations. I preferred the more advanced 8080 Microcomputer Experiments by Howard Boyet, which is also directed at the MMD-1. 

Video Series

MMD-1 Documentation

ROM Dumps

I dumped the Intel 1702A ROMS from my two devices. One had an original set, with the KEX in ROM 0 and the expansion IO Board in ROM 1. The other had a modified KEX in ROM 0 and an unidentified ROM in ROM 1. Looking at them briefly, it looks like the first one is a reworked KEX with IO related stuff added both in ROM 0 and ROM 1. I haven't reverse engineered it, I'd suspect it's a serial ROM monitor? The modified KEX works fine with the original keyboard and LEDs by default, except it comes up at address 002.000 by default instead of the original 003.000. Let me know what you find out if you reverse engineer it.

Reproduction Labels for the Breadboard

I made some reproduction labels for the breadboard. I printed them on a Brother label maker. The design files are in Affinity Designer format. My labels include the address lines wires that I added.

HP LED Modules Breadboarding Documentation

32k FRAM Board Module Documentation

In the video, we show how to extend the on-board memory to 32K of permanent FRAM memory by adding this cute module on the breadboard. You'll also need to wire a few more address wires to the breadboard to enable the full 32K. The board was designed by TubeTime, aka Eric Schlaepfer. The project is in KiCad format. The "fab" folder contains the gerbers ready to send to a PCB fabricator, we used PCBWay. This version is the final version and include the logic bug fix and the decoding of address bit A15. So no external logic gates are required as in the video, you should just be able to plop this in. We ended up not liking the extended pins shown on the picture (too flimsy, takes too much room on the side) and reverted to traditional 0.1" headers in the final version.

Serial IO Port Documentation

Documentation of my breadboard Serial IO.  Refer to the video for more details

MMD-1 BASIC

Here is some documentation from our modified Altair Basic that can run from the MMD-1. It's a pretty heady hack, refer to the videos to make sense of it.

Intel 1702 ROM Programmer (by Matthew Millman)