Re: 8501 datasheet / information is wanted :)

From: Gábor Lénárt <>
Date: Sun, 3 Feb 2013 19:41:01 +0100
Message-ID: <>
On Sun, Feb 03, 2013 at 06:54:06PM +0100, Gerrit Heitsch wrote:
> >I've decided to try to build some minimal system based on a 65xx CPU. The
> >"best" CPU I have for this purpose seems to be a 8501 from an otherwise
> >non-working C16, fortunately it was sockected (I am not sure if it's a
> >standard thing being socketed or not).
> Problem is, the 8501 is prone to die easily. So the reason why this
> C16 is not working might be that the 8501 is dead.

Maybe, however I have two of them, so I believe in my luck. I have even
found an older mail here about the heating problem (a not needed resistor on
the mask of the CPU or so?), but since I would drive the CPU at a constantly
1MHz clock (afaik in C16/Plus4 it is clocked at 1.76MHz during the TED
video blanking periods), I guess I won't fry it if they managed to survive
their lifespan in their original place (Commodore 16) ;-) I also have a
Commodore Plus4, but I wouldn't like to cannibalize it, as it's a working
machine otherwise. As I've read many reports about dead TEDs too, I thought
the unworking state of my C16s can be caused by TEDs as well, so I can have
to hope to find the CPUs working actually. I would try to test them with
the "NOP executing" breadboard config :) however my first problem was even
the unknown pin-out of 8501 ... The test circuit has UM6502 currently, so
some modification is needed, I guess (I even don't know if 8501 needs two
phase clock or not, etc).

Anyway I don't think that 8501 is _that_ easy to die, as I was in a
"computer camp" in my teenager period having about 40 machines of perfectly
working C16s ... :) :) Hungary is somewhat "famous" for having more
C16s and Plus4's than the world's average density of these machines :)
Actually I got these C16s for free as an "extra" when I bought a Plus/4 some
years ago.

> >Also what seems to be a magic for me: it's often quoted as an imporant
> >feature of 8502 that being capable running on 2MHz, not only 1. However even
> >8501 runs at 1.76MHz (during blanking times, when TED does not need to
> >access memory?) in Plus4 so 8501 is allowed to run over 1MHz cleanly, it
> >seems. Does it mean that I can run 8501 at about 1.7MHz constantly without
> >problems, or this is only the effect that the average clock of a 8501 in C16
> >is about 1MHz (slightly more though) and 1.76 is only the peak?
> If you tell TED to disable the screen output (border color displayed
> on the whole screen), the CPU will run on 1.7 MHz all the time. The
> only exception being the 5 DRAM refresh cycles happening every can
> line.

Well, yes, just I thought that maybe 8501 is not stable enough to run
constantly at 1.7MHz clock. And I was somewhat surprised as the "original"
6510 (and 6502) is specified as an 1MHz clocked CPU, while 8502 is being
2MHz, so I thought 8501 should be 1MHz, but this ~1.7 seems to be strange for
me. Maybe is it clocked at an "unofficial, out of specification" clock in
C16&Plus4? I am just curious here, this is one reason I would love to see
the "official" MOS 8501 specification/datasheet.

> >Currently I am "playing" with an UM6502 (made by UMC) but I would be happy
> >to use 8501 instead (the integrated i/o port is great for a hobby project
> >like mine!), but I would need some information/datasheet first to understand
> >the differences between 8501 and 6502 (there are much more information
> >available on 6510, that's why I wamt to compare 8501 with that).
> If you really must use a 65xx with integrated I/O, you should use
> the 6510/8500. Much easier to get and stable. Also most of them

I see. However I wouldn't enjoy to cannibalize my C64s for 6510 and also
(afaik I can rembeber, I am not sure) the CPU is not even socketed there by

> should be able to run on 2 MHz. I have a 6510 stamped with an 'A',
> indicating 2 MHz capability.
> Otherwise... How about using a 6502, a 6532  and an EPROM for the
> code? The 6532 will give you lots of I/O, timer and 128 Bytes of
> RAM.

Well, my needs is about what I have ... Unfortuntely it's almost impossible
here to get 65xx parts, but I managed to get an UM6502 (this was my original
"playground") and now I've just realized that I also have two 8501s in two
C16s. The best solution would be get a 65C02 or 65C816. The integrated I/O
is just because that it can simplify my situation with my very first 65xx hw
project, I would use anyway some more modern CMOS part for the next one.

- Gábor

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Received on 2013-02-03 19:00:30

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