Re: CIA old/new?

Not every detail in the design is clocked, some delays just happen because of 
gate propagation delays - and when the process changes, those delays may 
change as well. The well known "grey dot" the new VICII produces are related 
to exactly the same thing.

Am Sonntag, 3. Januar 2021, 21:37:35 CET schrieb Francesco Messineo:
> Ok, but how did they manage to introduce an error in the IRQ triggering?
> I thought the transistor "map" was the same, just different process
> 
> On Sun, Jan 3, 2021 at 9:32 PM Gerrit Heitsch <gerrit_at_laosinh.s.bawue.de> 
wrote:
> > On 1/3/21 9:15 PM, Francesco Messineo wrote:
> > > Hi all,
> > > I always thought the old (6526 I guess) and the new (8521) CIAs were
> > > identical, then I've seen this code:
> > > 
> > > testCIAVersion:
> > >      //; Set NMI vector
> > >      lda #<continue
> > >      sta $fffa
> > >      lda #>continue
> > >      sta $fffb
> > >      
> > >      lda #$81  //;also don't forget to set mask. Setting $01 to an
> > > 
> > > appropriate value will also help :-) (Bitbreaker/Oxyron)
> > > 
> > >      sta $dd0d
> > >      
> > >      //; Set timer to 5 cycles
> > >      lda #4
> > >      sta $dd04
> > >      lda #0
> > >      sta $dd05
> > >      
> > >      //; Clear the detection flag
> > >      sta oldCIA
> > >      
> > >      //; Fire a 1-shot timer
> > >      lda #%10011001
> > >      sta $dd0e
> > >      
> > >      //; This should be interrupted before the INC
> > >      //; only if it's a newer chip.
> > >      lda $dd0d
> > >      lda $dd0d
> > >      inc oldCIA
> > >      
> > >      jmp * //; just in case
> > > 
> > > So it seems the NMI triggered by some CIA revisions has an off-by-one
> > > cycle error?
> > > Can anyone explain what's the difference between the two CIAs?
> > 
> > NMOS vs. HMOS-II process and die shrink.
> > 
> > For a while the HMOS-II version was labeled '8521R0' before MOS went
> > back to the '6526' marking. You can tell by the datecode (end of '86 or
> > later = HMOS-II) and the '206A' or '216A' right of the datecode.
> > 
> >   Gerrit


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