Re: HMOS VIC sparkles

On Sat, Jul 27, 2019 at 07:08:57AM +0200, Gerrit Heitsch wrote:
> On 7/27/19 1:03 AM, Segher Boessenkool wrote:
> >I don't think there is a difference between 65xx and 85xx VICs here.
> >The main difference is these are used on different boards, with different
> >PLA or equivalent circuitry, which has a much bigger timing difference
> >than the different NMOS chip generations do (or actual changes on the
> >chip layout, which there are a few, although not many).
> 
> We had a discussion about this years ago and I supplied a lot of scope 
> plots (I still have them).

So do I :-)  Domain name changed; now it is
  http://segher.wiibrew.org/c64/plots/vic.html

> Your conclusion was that the HMOS-II VIC is 
> faster so you get to see the internally precharged lines.

Different board, different PLA.  But also that the chip may be slower,
yeah, giving slower AEC output, esp. rise/fall time.  I completely
forgot about that part :-)

Either there is a bigger load on the AEC signal on the new board, or
the driver on the AEC output from the 8565 VIC-II is weaker than on
the old chip.

The end result is that #CS is about 35ns earlier on the new system,
so it is "visible" in the chip before R/#W does (R/W# is one of the
things that gates the internal address bus from being driven from
the data pins, you get a pull-up on the internal data bus if nothing
drives it).  The AEC is maybe 10ns or 15ns of that; the rest is
other factors that slow down #CS.

> TED has the same sparkles BTW, but they are a different color.

Light green?


Segher