Re: Hardware emulation of 6509 using 6502?

On 03/15/2018 03:13 PM, silverdr@wfmh.org.pl wrote:
> 
>> On 2018-03-15, at 14:24, Segher Boessenkool <segher@kernel.crashing.org> wrote:
>>
>> The 65xx SID has highly non-linear "opamps".  The 85xx fixes that.
>> Not everyone likes it, of course.
> 
> It fixes also the bad clicks during volume change for example. Or is it the side-effect of the above?
> 
>> On later C64 machines the CS line to VIC goes active earlier,
> 
> Is it because they inaccurately emulate the original PLA in a completely different chip?

The behaviour is the same, but the logic is faster, so you get the 
output signals earlier in the clock cycle. So from a digitial point of 
view it behaves the same, from an analog it doesn't

> 
>> causing
>> the sparkles.  A little cap (from CS to ground) solves this.  There is
>> no difference between the 65xx and 85xx VIC here.
> 
> Even sparking aside, the picture is noticeably different. I don't say "better" or "worse" but it is different.

You get picture differences between the 6569 revisions as well, with the 
6569R1 sticking out due to having only 5 luma levels.

If you go by 'original experience', you have to use a 6569R1 since 
that's what you got at the beginning...


Oh, and I'm not going to get an Ultimate-64. Part of the fascination of 
these old systems is that if they stop working, I can hook up my scope, 
warm up the soldering iron and fix them myself. You won't be able to do 
that with the Ultimate. If it stops working, you're SOL.


  Gerrit