Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!oliveb!tymix!antares!tardis!jms
From: jms@tardis.Tymnet.COM (Joe Smith)
Newsgroups: comp.sys.amiga
Subject: Re: New Agnus
Summary: Current motherboards only handle 1 meg chip ram
Message-ID: <114@tardis.Tymnet.COM>
Date: 9 May 89 06:36:47 GMT
References: <1562@hub.ucsb.edu>
Reply-To: jms@tardis.Tymnet.COM (Joe Smith)
Organization: McDonnell Douglas Field Service Co, San Jose CA
Lines: 18

In article <1562@hub.ucsb.edu> dougp@sbphy.ucsb.edu writes:
>    It seems definate that the new chip can handle 1 Meg of chip
>ram, but can it handle 2 Megs? (2 Megs is the address space set 
>asside in the Amigas memory map for chip ram.)

The A2000 and A500 motherboards can only handle 1 megabyte of chip RAM.
That's because only address lines A1 thru A19 go to Agnes' socket.  A1 thru
A18 are pins 60 thru 77 respectively and A19 is pin 59.  
   2^19 = 512K words = 1024K bytes = 0x000000 to 0x0FFFFF.  
Even though expansion RAM doesn start until 0x200000, there is no way the
custom chips can access locations from 0x100000 to 0x1FFFFF because address
line A20 doesn't go to Agnes' socket.  I have no idea what Commodore is
planning for that unused address space.
-- 
Joe Smith (408)922-6220 | jms@antares.Tymnet.COM or jms@tymix.Tymnet.COM
McDonnell Douglas FSCO  | UUCP: ...!{ames,pyramid}!oliveb!tymix!antares!jms
PO Box 49019, MS-D21    | PDP-10:JMS@F74.Tymnet.COM  CA license plate:"POPJ P,"
San Jose, CA 95161-9019 | narrator.device: "I didn't say that, my Amiga did!"