Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!lll-winken!uunet!cbmvax!daveh
From: daveh@cbmvax.UUCP (Dave Haynie)
Newsgroups: comp.sys.cbm
Subject: Re: what is this chip(65C802)
Message-ID: <6460@cbmvax.UUCP>
Date: 30 Mar 89 18:53:28 GMT
References: <41063@tut.cis.ohio-state.edu>
Organization: Commodore Technology, West Chester, PA
Lines: 57

in article <41063@tut.cis.ohio-state.edu>, calhoun@cis.ohio-state.edu (robert r calhoun) says:

> 	While I was researching the 6502, I came across	a 65C02 which is a 
>	CMOS 4MHZ version of the 6502.  I noticed also that there is a 65C802.
>	From what I know, this appears to be an	Advanced CMOS 8MHZ processor.  

Sounds like you've been reading GTE databooks.  One caution -- don't believe
everything you read.  While these databooks often show the timing for parts
in a wide variety of speeds, that doesn't necessarily mean that such parts
are actually available.  Last time I looked, GTE listed 65C02s up to 4MHz and
65C802s and 65C816s up to 8MHz, though they only had 4MHz versions of the
latter, and no real yield on the former at 4MHz (they probably have the
4MHz 65C02s by now...).

>	He now wants me to rearrange his C64 to use the fastest 65??02 I can 
>	find.  If the 65C802 is truly an 8MHZ processor I calculate that he 
>	will need 100ns memory chips.  I don't recall seeing 64k 100ns chips 
>	so I guess I'll have to make it accept 256's.  

Someone currently sells a little accelerator for the C64 that plugs into
the cartridge port and runs up to 4MHz (check the C64 magazines).  You can't
run at 8MHz using dynamic RAM; 100ns is just the RAS access time.  A minimum
cycle time for such a part is 180ns.  Also consider that, even though the
cycle time of an 8MHz part (which you probably can't get anyway) is 125ns,
you can only use a fraction of that time for your memory access.  There's
a wait for addresses to be valid (probably around 1/4 or so of the cycle),
and a setup time for data to be valid before the processor clocks it in.  Not
to mention any external logic needed to multiplex the address lines from the
CPU to the DRAM and for decoding.  The 4MHz C64 add-ons use static RAM,
probably 100ns parts.  Note also that since the C64 uses a 6510, which has
an on-chip I/O port, you'll have to come up with some way of emulating that
port.

> 	With this idea, I would like to know if there is
> 	a faster C64 video chip so that I won't have to continuously write
> 	a copy of video ram to the old 150ns RAM.  The wait states would be
> 	too harsh to consider.  Anyone who has tried any of these, I would
> 	greatly appreciate learning from your experiences and mistakes.

There are no faster VIC chips.  You'll have to come up with some clever
scheme to make this work correctly.  I'm not exactly sure what the folks
who make these accelerators do, but there are options.  One option would
be to make like an Apple II GS.  Whenever your fast CPU writes to memory,
you slow down to 1.02MHz and write to both normal C64 memory and your fast
static RAM.  Same thing happens for read or write of I/O devices.  For
straight memory reads, you can read full speed from your static RAM.

Needless to say, this isn't a one-afternoon project.  Such an accelerator
is going to require some clever hardware design.  Once it's done, you'll
no doubt learn about "software timing loops" when a good portion of the
C64 programs you have don't run properly.  Folks are selling these accelerators
for more that the cost of a C64; much of that selling price is the cleverness
you're buying.
-- 
Dave Haynie  "The 32 Bit Guy"     Commodore-Amiga  "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: D-DAVE H     BIX: hazy
              Amiga -- It's not just a job, it's an obsession