Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!batcomputer!munnari.oz.au!yoyo.aarnet.edu.au!sirius.ucs.adelaide.edu.au!adam.adelaide.edu.au!phil From: phil@adam.adelaide.edu.au (Phil Kernick) Newsgroups: comp.sys.amiga.programmer Subject: Re: CIA register Message-ID: Date: 16 May 91 07:27:22 GMT References: <1991May14.164909.19186@NCoast.ORG> <1991May15.183635.24595@wehi.dn.mu.oz> <91135.204206FERZAN@TREARN.BITNET> Sender: news@ucs.adelaide.edu.au Organization: University of Adelaide, South Australia Lines: 26 Nntp-Posting-Host: adam.adelaide.edu.au FERZAN@TREARN.BITNET writes: > Can anyone explain the memory overlay bit > in the CIAA chip ? > I didn't find any info in Amiga Hardware Manual and > Mapping The Amiga book .. > But I think this bit sets the ROM start address to 0 > Really ? It probably does. This is just sheer speculation, but I suspect that it is set when the machine is reset, and points the ROM at 0 so the processor will be able to pick up the initial PC from address 0 and SSP from address 4. It almost certainly resets after this and the ROM initialises all of the standard 68000 vectors and then starts the OS. Hope this helps, Phil. -- o| /// Phil Kernick EMail: phil@adam.adelaide.edu.au |o | /// Departmental Engineer Phone: +61 8 228 5914 | o| \\\/// Dept. of Psychology Fax: +61 8 224 0464 |o | \/// University of Adelaide Mail: GPO Box 498 Adelaide SA 5001 |