Re: Overclocked Deluxe - limited success

From: Rodger Boots <rlboots_at_cedar-rapids.net>
Date: Fri Apr 27 2001 - 04:01:55 EDT

Neil Bradley wrote:

> Well, I tried overclocking the Asteroids Deluxe board and here's what I've
> found. I cut the trace between the CPU and the solder points so I'm not
> increasing the clock to any other circuitry - only the processor. Then I
> jumpered pin 37 of the CPU (clock) to pin 14 (6Mhz), pin 13 (3Mhz) and
> eventually back to its original home at pin 12 (1.5Mhz) on chip C3.
>
> @ 3Mhz - I get 5 high tones then 1 low tone, and this cycle completes. I
> don't have a diag manual for Asteroids Deluxe. Anyone know what this
> means? RAM Error perhaps?
>
> @ 6Mhz - Nothing happens.
>
> I'm not sure what the problem is, but I have a few hunches:
>
> * How fast can the 2114s on this board actually run? Is 6Mhz too fast for
> them to keep up? Hm.... 6Mhz=166ns if it can do a SRAM every clock. Is
> this possible? I've found some 2114s that are rated to 200ns. Is it
> worthwhile to swap them out?
>

The address to the RAM from the 6502 isn't guaranteed valid until well into the
cycle. Your 166 nS is probably dropping to well under 100 nS of valid address to
valid data fetched time.

If you're even going to try overclocking you will need MUCH faster RAM and EPROM,
not to mention replacing the stock NMOS 6502 series processor with newer, faster
CMOS parts.

>
> * Are there any other circuits that are connected to the data/address bus
> that might also be speed sensitive? The vector SRAM?
>
> * Maybe the CPU can't keep up?
>
> Any help would be greatly appreciated...
>
> -->Neil
>
> -------------------------------------------------------------------------------
> Neil Bradley Play a song wrong once and it's a mistake.
> Synthcom Systems, Inc. Play a song wrong twice and it's Jazz.
> ICQ #29402898
>
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Received on Fri Apr 27 04:12:05 2001

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