Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!decwrl!pyramid!leadsv!practic!vlsisj!davidc
From: davidc@vlsisj.VLSI.COM (David Chapman)
Newsgroups: sci.electronics
Subject: Re: Z-80 NMI
Summary: put it in a loop
Message-ID: <15519@vlsisj.VLSI.COM>
Date: 14 Mar 90 06:09:13 GMT
References: <5539@bgsuvax.UUCP>
Reply-To: davidc@vlsisj.UUCP (David Chapman)
Distribution: usa
Organization: VLSI Technology Inc., San Jose, CA
Lines: 18

In article <5539@bgsuvax.UUCP> nandan@bgsuvax.UUCP (rajesh Nandan) writes:
>If the Z-80 is executing "executable" codes the NMI works & forces a jump to
>0066H but when I make it "HANG" by jumping to a "nonexecutable" part of code 
>the NMI DOESN'T work even though the RTC(58167) chip connected pulls the pin 
>low. ie:- the NMI doesn't work if it has hung. 

Executing random code could possibly scramble the internal state of the
processor by executing illegal instructions.  There often isn't any guard
against executing undefined instructions on these 8-bit processors.

It's *never* a good idea to execute random instructions.  Put the processor
into a tight loop instead.  You may even be able to halt it; I don't remember
whether a Z80 can be awakened from a halt or not.
-- 
		David Chapman

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