SV: Re: [sdiy] Roland DCOs

[karl dalen]

Just as a tiny side note. Thats Intels original, we have no idea if 
the silicon where redesigned coming from other wendors and there are many
to chose from. Also there are plenty of clones under different labeling,
altought 8253, 8254 was the system timer chip in 8088 286, 386 PC's for
quite some time. Inside those old PC's there are loads of these chips
in them particularly 8088-86. Anyway hilarious bugs alright!!!

Reg
KD

--- Ingo Debus <debus at cityweb.de> skrev:

> 
> Am 25.02.2008 um 22:34 schrieb Tom Wiltshire:
> 
> >>>
> >>> What I wanted to know is if anyone has built a DCO along these  
> >>> lines, and what they discovered. I've wondered about doing it  
> >>> myself since the 82C54 triple counter chips are only a few pounds
> >>
> >> AARGH! The nastiest chip I ever came across!!
> >
> > I'd be interested to hear why. It looks like a pretty straight- 
> > forward IC from the datasheet.
> 
> Didn't think I'd ever touch that datasheet again, but here it is:
> http://download.intel.com/design/archives/periphrl/docs/23124406.pdf
> 
> Here's the crucial sentence, page 16, note 3:
> "Low-going glitches that violate tPWH, tPWL may cause errors  
> requiring counter reprogramming."
> 
> Yes, that's very true, I found it out the hard way. This chip can  
> forget what it was programmed to do. It simply stops working and has  
> to be re-programmed. Doesn't happen very often (seldom enough that I  
> missed that bug in the first prototypes), but it does happen.
> 
> I couldn't ever catch any short glitches in the clock signal (only a  
> 100MHz scope back then). But note there's also a tWC and tWG  
> specified. So not to violate that you'd have to watch the clock or  
> gate when accessing the '54 from the microprocessor. That's almost  
> impossible to do. I suspected that I didn't violate the tPWH, tPWL  
> specs but rather the tWC and tWG which crashed the chip.
> 
> Ingo
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