Re: Looking for a VHDL forum or individual help

From: André Fachat <>
Date: Mon, 23 Aug 2010 22:03:21 +0200
Message-ID: <>
> > How would the NMI even work if it is implemented as level triggered?
> > It's _non_ maskable.  If strictly level triggered it will just endlessly
> > retrigger the interrupt with no chance to ack, no?
> and thats what happens actually, and its why there is a RC element wired
> to 
> the restore key :)

The RC element is there to avoid multiple edges by smoothing out the signal, so only one edge is detected per key press (which does not necessarily work, as pointed out in other posts)

But if NMI would be level triggered, you would trigger a new NMI in each cycle - you would not have any chance to actually execute the NMI routine at all.

My assumption is that they detect the NMI level synchronously at, say phi2 going high or going low, and then detect the level change. Which is basically an edge trigger. Only that it is - technically - different from an edge trigger that triggers asynchronously directly on the NMI level change.


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Received on 2010-08-23 21:00:06

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