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From: davel@hpvcla.UUCP (davel)
Newsgroups: net.micro.apple
Subject: Re: Interupts on a apple ][+
Message-ID: <4400003@hpvcla.UUCP>
Date: Wed, 6-Nov-85 11:55:00 EST
Article-I.D.: hpvcla.4400003
Posted: Wed Nov  6 11:55:00 1985
Date-Received: Tue, 12-Nov-85 04:43:06 EST
References: <76@noscvax.UUCP>
Lines: 14
Nf-ID: #R:noscvax:-7600:hpvcla:4400003:000:554
Nf-From: hpvcla!davel    Nov  6 09:55:00 1985



In a II+ the monitor code that "catches" the interrupt uses the areg to
determine if the interrupt is hardware or a break insruction, as a result
the areg gets trashed.  The good news is that before the above test is made
the areg is saved in location $45. The bad news is that the areg does not
get restored from $45 on an RTI, you have to restore areg with an LDA before
the RTI.

My disclaimer: I am reciting this info from memory, and it has been a while,
so some of the nitty-gritty details may be incorrect.

				Dave Lowe
				hp-pcd!hpvcla!davel