Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: Notesfiles; site hpvcla.UUCP Path: utzoo!watmath!clyde!cbosgd!ihnp4!houxm!vax135!cornell!uw-beaver!tikal!hplsla!hpvcla!davel 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