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Hardware - Prototype PI9
Name:Prototype PI9

Prototype PI9
Anders Carlsson owns this prototype machine tagged "PI9".

This is the first rough description he has originally posted on the CBM-hackers mailing list, then all the thread's discussion here evolved in answers, clues and more:

"I have come across an unknown, TED based motherboard which I would appreciate pointers about. It only has 14 chips, named as following:

U1 = NE555N 8144
U2 = P8214A DM7406N
U3 = U4LS139N 8137 SA
U4 = empty
U5 = INMOS 8329-A IMS 2629P-15 C1059A KOREA
U6 = INMOS 8329-A IMS 2629P-15 C1065A KOREA
U7 = 74LS257AN 8216 SA
U8 = ?? (unnamed logic chip, perhaps CPU?)
U9 = empty
U10 = 27128 EPROM marked "TED LO"
U11 = 2764 EPROM marked "TED HI LO-V1.0"
U12 = 2764 EPROM marked "TED HI HI"
U13 = 74LS257AN 8216 SA
U14 = MOS 7360R4A 4183 (TED)


Where is the 7501/8501 CPU, is that the unnamed one in U8? As you can see, there are two diodes running between some pins on the TED chip, and some extra (cut?) wire near the cartridge port. Later I can look up exactly which pins the diodes go between.

On the under side of this motherboard, it is stamped "Q.C INSP'D AUG 3 1983". Is this normal for an early TED line motherboard, given that they started to sell sometime during 1984 if I recall correctly? I was thinking maybe this is some prototype.

I tried to power it up, despite lacking some chips. It makes a faint buzzing noise. Using a video cable, the monitor detects power on, but no picture. Using RF, there is no signal at all, at least not at UHF 36. I noticed the RF modulator has a small switch, which suggests it may be a NTSC unit rather than PAL?

I see that Zimmers have some schematics for different Plus/4, Commodore 16 and 116. Which one would best match this board, and how can I find out which chips should go into U4 (logic gate?) and U8 ? Probably it'd be tricky to get working anyway, given that fully equipped Plus/4 tend to break in CPU and TED chips, much less a loose board that for some reason has been sitting on a shelf for 15-20 years."

Bil Herd Did Just Tell You
Bil Herd, principal engineer in the Commodore 264 series development, has confirmed it is his own handwriting on the prototype board.

Moreover, there are several matchings between the so called PI9 Prototype, and the early prototypes he describes in the famous book "On the Edge".

Finally, here comes direct words from him:

"At first I thought it was a C64CR type thing but this looks like a member of the TED family, probably a C16. It has the standard joystick ports so its one of the later strange things like the C16 that magically appeared. The two resistors on the chip mark it as a TED where the test mode pins were higher impedance than predicted by the chip designers and a strong electric field would freeze the counters. The diodes near the keyboard connector also make it a TED, though there is a chip missing from my last rev of it, this may be a non-production board (in fact none with the resistors would have made the airwaves). Since there are
only two chips that look like memory, it is probably 16Mb.
Clearly a TED, the unnamed 40pin chip is something like a 7501 cpu which is a processor with a gated r/w line to hold the line valid through the DRAM cycle. I added U1 myself as the design when I got to CBM tried to use the 7406 as a level detecting reset circuit.
The design also called for the data lines to go directly out the keyboard port (hence diodes, Germanium no less, to keep the data lines from shorting out when you pressed multiple keys) which was also the joystick port. the problem was the noise the joystick port would pick up would create sparkles in the picture due to blown data. I added an 8 bit latch (nmos MOS 8529 or something like that) to isolate the data lines form the keyboard/joystick."

Later, Bil Herd has added a page on his own site, at
Accordingly to that, Bil Herd added some more notes on Facebook's comments:
"I think the user port was a 264 creation, especially when we hooked a real UART to it. This would have been a predecessor to the C116. In a way this is a testament to Ira Velensky the case designer for the C116; this is what the raw material looks like and then the C116 was actually like a small work of minimalistic art, right down to the mini-dins and the battles they caused.".

Anders Carlsson dumped the TED prototype: get the romset here.

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