Motorola MEK6800D2 computer

This Web page last updated date Aug 27 2013.

Introduction

[Motorola 6800 D2 manual]

I acquired this 6800 D2 Evaluation Kit many years ago. In March 2013 I was going to show it at the Trenton Computer Festival 2013, but it was rejected because it was not running, and I had no time to check it out. But I took some time after the event to repair it, and I was surprised that it came up without a lot of fuss. The photo at left shows the User's manual and is also a photo of the keyboard & display of the D2 kit. I sold this kit in Aug 2013.

This is part of other vintage computer repair and restoration work I've done. I did some work on a related 6800 system from SWTPC, but it's not had power as of mid-2013. - Herb Johnson

D2 board

[Motorola 6800 D2 CPU] [Motorola 6800 D2 kbd/disp]

To the left is the D2 CPU board. It has the usual sorts of things that an 8-bit CPU family had in the 1970's. The 6800 CPU chip, the 6810 128-byte RAM, the 6820 PIO parallel I/O chip. Also a Motorola MIKBUG ROM, and a Motorola brand crystal/clock chip in the metal can. There's a serial UART chip, called an 6850 ACIA,

To the right is the display and keyboard, connected to the CPU board by a flat cable. There's six 7-segment displays, and a hex keypad with function keys. The red flatcable on the left of the display board, connects to the white connector on the right of the CPU board.

Restoration

[Motorola 6800 D2 operation]

When I got the board, a chip was missing, and it was an odd one - 74155, a kid of 3-to-8 decoder. I was fortunate to have a used "pull" from a collection I bought last summer. Some of the through-holes on the PC board seemed to need some solder, and a few components had cold-solder joints upon visual inspection. I made these repairs. After some fuss with wall-warts, I decided to use an old open-frame power supply for the 5 volts needed.

Much to my suprise, when I powered up the first time, there was a display, and some response! I checked for loose chips in their sockets, and when I tweaked a few of them I got some instability. A few rounds of such work and the board appeared stable. I punched some keys and got some results - I took a photo QUICK before it blew up!

Of course...I had not read the user's manual in about 30 years, so I didn't know how to run it. But like many "evaluation board" kit manuals, the keyboard functions were described and not hard to use. "M" is for memory, "E" is for escape (from the current operation), "R" shows the registers (as dumped into memory), "G" is for go or execute at. You can also set breakpoints and remove them, and step through execution. MIKBUG sorts all this out, and the source is listed in the manual. The schematic for the CPU is here and the schematic for the keyboard/display is here.

The manual even has a short program to add some values, and with a bug. Of course, you load the program, walk through it, and debug it - all described and simple enough to follow. Like many vintage computer manuals, you can find copies at bitsaver's various mirror sites.

I sold this kit in Aug 2013.

- Herb Johnson


Herb Johnson
New Jersey, USA
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