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Amiga computer related discussion => Amiga Hardware Issues and discussion => Topic started by: amigan24 on May 20, 2009, 08:46:32 PM

Title: Possible to use 8375 Agnus from a600 on rev 5 A500?
Post by: amigan24 on May 20, 2009, 08:46:32 PM

Hello there...

I just did the jumper/cut mod on my rev5 A500 for 1 meg chip ram out of sheer boredom and much to my dismay it worked when using the stock 8370 Agnus.

Well, it worked until I ran an old version of octamed, which crashed almost immediately. I decided to pull the 8375 Agnus from a broken a600 and try to "plug and play" but there was no screen...just black. I did some reading and I see that it should just work:

http://www.amigau.com/natamiga/t-agnus-installation.shtml

...but it does not. Is there anything I might be missing here?

Also, the site looks great!

Title: Re: Possible to use 8375 Agnus from a600 on rev 5 A500?
Post by: Zac67 on May 20, 2009, 09:46:05 PM

The 1 MB mod makes the expansion look like chipmem for the OS - however, if you've got an old Agnus in place, there's no way this would work properly as the registers are too small to address the correct data. Screen corruption, data corruption on floppies(!), Copper runaways and complete memory corruption when using the Blitter are bound to happen.

8375 is the most ambiguous labeling CSG used; there are various pinouts under that number. There was a good thread here comparing the different versions 1-2 years ago; BBoAH isn't too acurate in that respect. The A600 version is the same as the A500+ one, but it doesn't work in an older A500 without heavy modifications.