Re: Broken TED for visual6502.org

>>> Hm, on the lower row of pads I find damage that looks very similiar,
>>> just not as extreme though.
>>
>> I don't see anything like it?  At many places the metal is cracked  
>> and
>> darkened, but near A7 it is totally black and not cracked.
>>
>> But who knows :-)
>
> Could be... But what caused the driver for A7 to die in that  
> fashion though? I should have tested all the signals before mailing  
> in the CPU to see if any of them were dead.

A short circuit on the pin: if something (external) drives the address
line high while the CPU pulls it low, a nice big large current goes
through that big FET where the metal turned black.  It's not built
for such large currents, it's too high resistance for that, you get
heat, stuff melts and whatnot.

> If MOS stuck to the usual numbering scheme, it would mean the 8500  
> came first, at least as far as the design is concerned. Also, they  
> did manufacture the 6510 and the 8500 in parallel for a while. I do  
> have an 8500 with a 1985 datecode and a few 6510 with 1986  
> datecodes. I wonder why they did it... Reliability issues that  
> caused them to go back to the 6510 until they were cleared up?

Maybe they simply needed more CPUs than their 8xxx production lines
could make at the time.  They also used various fabs in various
countries, it stands to reason that not all of those were upgraded
to the new  process at the same time (if at all).

>> These additions can easily be made to a 6502 to create a 6510,  
>> without
>> adding a whole wide ring of stuff around it all, except obviously for
>> the P port stuff itself.  The 850x is different of course, because  
>> the
>> pad drivers have to be a lot bigger relatively.  So I'd still like to
>> see what things look like on the 6510 :-)
>
> I'd like to see the 8500 or 8502 first to see if it's really just a  
> few minor changes.

Sure, I'd love to see those as well, but the 6510 has bigger differences
to both endpoints we have pics for so far (6502 and 8501).  And it's
historically more interesting.


Segher


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