Subject: Re: TWGS & WDC 65816 chip
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Date: 31 Oct 1999 15:17:41 GMT
References: <cornelio-3010991630090001@dt050n7c.san.rr.com>
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cornelio@san.rr.com (L. Cornelio) wrote:

>I am curious --I was reading an old issue, v2.1 of shareware solutions
>mentions that WDC was expecting at that time to release a 20 mhz version
>of the chip. Did that ever happen? Are there two chips still available? I
>usually see reference to 14 mhz, but  Trevor M. (hi Trevor!) reports his
>TWGS is running at 20 mhz w/ no problem except an incompatibility w/
>ramkeeper....

The 14Mhz chip IS the 20Mhz version.  Chips are rated
using testing equipment.  When Sanyo delivered the
new 65C816 that WDC comissioned them to do, it was
so good that the chips consistently passed the fastest
speed that WDC's testing equipment could test, namely
14Mhz.  However, the chips were even better than that.
Samples sent for testing at a lab outside WDC showed
that the chip could go much, much faster.  But without
an internal testing machine capable of going faster
than 14Mhz, WDC had to label the chips as 14Mhz.

Several years ago, a company called Creative Micro
Devices (CMD) designed an accelerator for the C64
(and later the C128) based on the 65C816.  The wanted
to run the accelerator at 20Mhz.  When they contacted
WDC, the company said to go ahead and run the chip
at 20Mhz.  But CMD wanted confirmation, so all chips
delivered to CMD are first tested at an outside lab at
20Mhz.

CMD has sold hundreds of accelerators and not a
single 65C816 has failed at 20Mhz.

Whether your 65C816 will run at 20Mhz depends
on the accelerator card.  Mine, for example, will
not run at speeds faster that 12.5Mhz even though
I'm sure the CPU itself can go much faster. Trevor's
20Mhz speed is unusual.  He must have a
particularly good accelerator in terms of the
tolerances of the other chips on the card.

Trevor's 20Mhz TWGS should definitely go into the
csa2 FAQ.  It shows such speeds are possible with
the new 65C816.  It just depends on your particular
TWGS or ZipGS whether or not you can reach that
speed.