Re: HMOS VIC sparkles

On 7/27/19 4:07 PM, silverdr_at_wfmh.org.pl wrote:
> 
> 
>> On 2019-07-27, at 07:08, Gerrit Heitsch <gerrit_at_laosinh.s.bawue.de> wrote:
>>
>>>> .. I just had a discussion about those sparkles with a friend and couldn't authoritatively answer. Because if the above is true, then the sparkles should be visible regardless of which VIC is being used, right? You mention yourself that "there is no differnce between 65xx and 85xx here". Or is this 0b1111 only inherent to HMOS VICs? The reason I ask is because I recall "fixing" the sparkles in one machine decades ago by doing some wiring and running 6569 in the narrow board. I don't think I delayed the CS (back then I surely didn't have any idea about what was causing them to appear).
>>> 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).
> 
> That's where I got stuck in the discussion as it doesn't explain why I was able to "fix" the sparkles by running 6569 in the narrow board.
> 
>> We had a discussion about this years ago and I supplied a lot of scope plots (I still have them). Your conclusion was that the HMOS-II VIC is faster so you get to see the internally precharged lines.
> 
> So this would be neither the board nor the VIC but the combination of the two that leads to the effect being visible? That would explain. I don't ever recall running it the other way around but might do at some point to verify. The discussion was that I was making VIC responsible and the other guy was blaming the board.

Well, it's not that hard to get a 8565 to run on an old board and the 
same for a 6569 to run on a new board.

For the 8565 you to bend Pin 13 out of the socket, connect it to Pin 40 
(+5V) through a Ferrit bead and put a ceramic 100nf cap between Pin 13 
and GND. The picture might be a bit dark since the pullup for the 6569 
is 470 Ohm while the 8565 expects 1 kOhm. (Located in the modulator)

For the 6569 you need a 7812 to supply +12V to Pin 13 and might have to 
change one of the electolytic caps to enable to voltage doubler on the 
25469 board to be able to supply 40mA.

  Gerrit