RE: 264 Series and their chips

From: Bil Herd <>
Date: Sun, 14 Aug 2011 14:05:18 -0400
Message-ID: <>
We did strip things as needed , my memory is that they used the
real-estate on the 7501/8501 for an unused register bit to implement more
with back-bias generation.   I remember walking down the hall and
overhearing a conversation that the test guy (named was Terry) that was
writing the  genrad test code for the 7501 test fixture was having trouble
with the Port 0 test.  I remember asking him if he knew that one of the
ports was gone and he lit up saying that  that was the problem.   He was
trying to rotate a bit all the way through the register and of course it
wasn’t making it.

So not only did we strip and change things on the fly, we dint have
mechanisms and documentation that kept up, our eye was on the clock and
foremost did whatever we needed to move the ball a few inches; if we made
it we would worry later about cleanliness.

Quick story about how we figured stuff out on the fly:  We were getting
black dots on the display of the early  TED/264, seemed to have shown up
when we married a PCB with keyboard early on.  I threw a scope on the
master clock and it was "freezing".  I licked my finger and went around
the pins of the ted chip and found a pin that would cause a beat pattern
of black dots on the display (clock was freezing at a 60 hz rate) when I
touched it with my other hand on the monitor itself.   I strapped the pin
to VCC with a Germanium diode to keep the pin from pulling higher than VCC
and the symptoms stopped.

I walked in on a croup of chip guys talking and literally said " let me
guess, you are using xxx pin to freeze the clocks for test initiation
purposes (tests need to start from a known place) by pulling it above Vcc"
The answer was "ummmmm yeah, howd you know?"  I showed them the problem
and how I had to shunt it, turns out there was two pins that they had done
this to.You can see two Ge's soldered to early Ted chips in pictures and
old parts.  Basically they learned what the hw already types knew which
was that  a high impedance pin acts as a "amplifier" , I.E. they didn’t
think there was any way a pin could go above VCC when the highest voltage
was VCC.

Bil Herd
-----Original Message-----
[] On Behalf Of Nate Lawson
Sent: Friday, August 12, 2011 2:16 AM
Subject: Re: 264 Series and their chips

On Aug 11, 2011, at 3:10 PM, Hársfalvi Levente wrote:

> On 2011-08-11 18:32, Gerrit Heitsch wrote:
>> So I noticed when I tried it yesterday evening... Oh well, another
>> pretty theory shot to hell...
>> The reason I came up with this idea was that I read a posting on this
>> list where someone stated that the 6510 and the 8500 have the full 8
>> bit port on die and that you could use some clever coding to
>> distinguish between a 6510 and an 8500. Go look for the thread called
>> '6510 and 8500 differences'.
> Ah, Nicolas Welte's findings about the unimplemented portbits of the
> 6510/8500 ( kind of stuff I like cbm-hackers for :-) ).
> Thinking it over, even that one seem to contradict with the idea of a
> full 8-bit port that was supposed to be implemented on the 6510/8500's
> die. Bits of the output register don't fade out by the corresponding
> I/O pins absence. That might rather suggest that MOS already had a
> 8-bit port equipped CPU design, maybe more than one CPU design with
> several features incorporated into the 6510 at the time they actually
> needed the 6510, and pasted/stripped parts as needed, with no care for
> leftovers (ie. those that didn't hurt them).
> It's interesting though, that they didn't change the design once they
> switched to HMOS-II. I thought that move needed a more or less
> complete redesign of the chip. Still, the artifact has been kept (it's
> only the manufacturing process that results in different time until
> the fadeout happens), which suggest they didn't change the layout.
> ...I'm really looking forward for this thing to be demistified.

In "On the Edge", one of the C64 engineers said they made the 6502 into a
core before creating lots of variants, such as the 6510. (I believe it was
Winterble, but not sure.) Anyway, since the 6502 was hand-drawn, I assume
what they did was reconstruct the gate design in more modern CAD tools to
allow it to be modified more easily. This also would allow them to change
processes, do design shrinks, etc.

HMOS is still an NMOS process, just with higher density. Most of the early
Amiga chips were HMOS too. I think it wasn't until Commodore started
outsourcing some of the chip production that they moved to CMOS.


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Received on 2011-08-14 19:00:12

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