Re: Looking for a VHDL forum or individual help

From: Marko Mäkelä <*msmakela_at_gmail.com*> Date: Mon, 23 Aug 2010 22:02:52 +0300 Message-ID: <20100823190252.GA2623@x60s> · msmakela_at_gmail.com

On Mon, Aug 23, 2010 at 08:22:18PM +0200, Groepaz wrote:
>> 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 :)

Not on the Vic-20, or the circuit is not working there. On the Vic, the 
RESTORE key can easily cause a condition that could be a stack overflow 
caused by triggering an NMI while the NMI handler is executing. Just 
press the key so that it barely makes contact, or press it repeatedly, 
and you will be greeted with a cleared screen and the READY prompt, as 
if you pressed STOP+RESTORE or executed a BRK instruction.

	Marko

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