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Z80 CPU
8080 CPU
6500 Series
6800 CPU
DG Systems
Bytemaster
System Cards
Keyboard
Printer A & B
Phideck
Disk Drives
Documentation
Software
Flyers
Magazine Ads
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| 6800 Processor Board
I built this board originally around January, 1977. Although I was
already an experienced electronics hobbyist, my experience with computers
was limited to keypunch and time share systems, and a little (whatever I
could get) at the local university. I had no experience programming in
machine or assembly languages. I had no trouble assembling the computer,
and other than a small glitch due to a shorted line on the video card
(direct from the factory--not a solder bridge!), the machine worked the
first time it was switched on. I promptly called DG to order up some
software, and was told that the only thing they sold was for the 8080 and
Z80. I felt robbed! I was told that there would be some titles
forthcoming, but none available just yet. I was pacified. I waited, but DG
never came through. Nothing was ever offered for the 6800 by DG. :(
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6800 Processor Board, Sort-of Restored
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| I chose the 6800 in the first place because I
had read several articles on microprocessor architectures, and after
careful consideration, concluded that the 6800 instruction set was more
understandable. And for me, it was. I found it quite easy to write
software for the 6800, and although I wished (in vain) for some DG
software, I got along fine without it, though not without trying to
exchange my 6800 at one point for a Z80! In a letter from Dick Bemis, my
proposal was declined, though I was offered a Z80 for bargain price, my
piggy bank was too small at the time, and I made due with the 6800. I'm
glad I did. :)
The 6800 was a dynamic processor, that is to say, when paused, all
address and data lines were invalid. It was capable of single-stepping,
but required latches to hold over the values for examination. This made
the 6800 a poor choice for any computer that required a front panel.
Motorola intended this CPU to load startup data from a ROM--they offered a
standard ROM operating system they called MIKBUG. The DG computer did not
use this ROM, and as a result, was incompatible with most off-the-shelf
software available, without modification. Life was tough for us poor DG
6800 owners!
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6800 Processor Board, Solder Side
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| Restoration
From the first time this card was powered up, until today, this board
has always worked. However, over the years, I modified this board
extensively. I added a piggy-back RAM card of my own design, I added a
MIKBUG ROM for greater software compatibility, and I over-clocked it by
adding a variable speed clock. (Mostly unsuccessful--the improvement in
speed was insignificant, the DG 6800 ran pretty much as fast as the chip
would go.) These are just a few of the mods I made--I did literally
dozens.
Back in 1986, I backed out all of my modifications in favor of the
original design. In the mid-nineties, I decided to do a cosmetic
restoration, and cleaned up the board as seen here. Can you spot any of
the remains? Probably not many, most of my mods were done by pulling chips
and plugging in the mods in place of various existing chips.
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6800
Processor Board, Layout
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| 6800 Card Information
6800_CPU_Construction.PDF
- My original CPU documentation, the schematic is in poor condition I'm
afraid, the result of unending use. I now have a better copy, but have
yet to do the scanning. One day...
See my Document archive for more related files.
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