CB< Commodore, TED, C116, C264, Plus-4, Bil Herd, Dave Haynie, Terry Ryan, Fred
TED Drawings from the 1980's




More from the 30 year old box that was once part of the contents of my desk back at Commodore Business Machines in West Chester PA in the middle 1980’s.

For those that don't know, the Plus-4 Series of computers released by Commodore around 1984 where internally known as TED which stood for Text Display as this was supposed to be more business oriented than the C64. Here are some schematics from those TED days, the full scans are linked at the bottom and I took some color pictures so the nature of these drawings could more easily be seen: I had used a cheapo red felt tip pen to make sure the draftsperson (Sue) would be sure to include the changes into the master drawing.

Full-size schematics in grey

In one drawing it can be seen that I had cut part of another schematic and scotch taped it on top of the drawing for inclusion into the master.  Looking at a black and white scan makes it hard to see what the very low tech approach was to getting these drawings done.  If your wondering where the fancy CAD stations are is in a largest home computer company (at the time) they didn’t really exist yet. 2 years later everything was in drawn in a CAD.... and then redrawn on paper, go figure.

Looking at the schematic above you can see on eof the first of corrected problems.  When first bringing up the system for the first time it would crash, the R/W line was low and after making sure it wasnt shorted to anything I added a pull-up, followed by the conversation with a chip designer:

<Me> Uh, did you guys pull up the R/W line internally?
<Chip Designer> No, why?

TED Reset Circuit

You may have heard how the original C116/TED didn’t have a dedicated reset circuit as Engineering had basically been told not to add any new chips at that point. I had proven that the original reset circuit just plain didn’t work right (turn the AC voltage down to 105VAC and then turn the power on and off and is would oscillate like Keith Emerson’s favorite Moog) and that we needed a dedicated chip.  I didn’t set out to use a 555, I thought about chips with hysteresis like the 74LS14, but  paranoia won out; I was about to make my first significant design decision that affects a couple of million units and so I went with the venerable 555 as I knew bad part tolerances wouldn’t keep it from working as a worse case.  For example if we would have tried to create a straight-up RC circuit with resistor values of 100-470K a CHEAP capacitor might have enough leakage that it never charges.   In the end I didn’t lose my job as had stuck to the real rule of not adding frivolous chips and stuff, something later TED’s could be accused of.

Here you can see the original circuit under the 555 addition.
(click picture for larger image)

16k – 64k Interoperability

Here is an example of a piece of schematic taped on top and marked up, this was the groundwork for a commonality when using various sizes of DRAM’s.  In affect this opened the door for a flurry of oddball designs that came late such as 232’s and C-16’s.

Power Supply

We made the decision to use AC for the support voltage instead of DC.  By making the supply C64 compatible (ah, the real reason) we had tons of them available for early production phases up until someone made connector square. If you look at the leads of the electrolytic capacitors you can see where the connection has been redrawn to indicate to the PCB layout guy (Fish) to make the trace go to the cap first and then the rest of the board,

TED Reset Switch

Here I drew in a switch and instructed the Drafting Dept. to look up a previously used part.  The problem I have 30 years later is I don’t remember the C-64 having a pushbutton switch.  Anybody know what the heck I was referring to?

Ferrite Beads Everywhere

If you have seen the C116 Video and I mention that the ferrite beads is one of the telltale signs that I had worked on the design, here in the drawings you can see the liberal placement of lots of little rectangles representing where a Ferrite Bead needs to be added to the drawing. (I left it to the drafting department to create and track the designators FB1, FB2, etc.)  I forget if the ferrite to ground survived the cut, there are two schools about putting some impedance between the assembly and ground: do you want to try and ground the assembly better or risk contaminating the system ground too much.

From 65xx to 75xx

And finally one day the uProcessor got a formal name referring to it’s newer technology by the 75.  Eventually it migrated to the newer 85xx family.

Full-size schematics in grey

 Much thanks to Mike Naberezny and his father for the work doing the scanning, and to Steve Gray for hooking me up with Mike and to David Wood for touching up the images..


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