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Author Topic: A500 CPU piggyback RAM not the best?  (Read 2564 times)

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Offline hoptoitTopic starter

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A500 CPU piggyback RAM not the best?
« on: October 13, 2010, 07:02:12 AM »
Looking to track down a good RAM upgrade  for my A500. I was planning on finding a CPU piggyback expansion until I  found this post:

Quote
Generally the best way to combine expansions is to not use ones that  mix  address space on different buses. i.e. trapdoor expansions should  stick  to the trapdoor Slow RAM portion of the memory map, and the  CPU-only  portion should go on either a CPU piggyback or on the sidecar.  

CPU piggyback expansions are particularly problematic because they, by   their nature, can muck with the entire memory map that the CPU sees. I   strongly recommend that the only expansion you place there be a CPU   card, and if it has any RAM on it it should be true 32-bit RAM that the   rest of the system can't see anyway. If you put anything 24-bit on the   CPU socket, don't put anything on the side expansion slot.  Well-designed  stuff should play nicely via autoconfig, but there's no  way to  guarantee this will happen. There were a few 32-bit CPU cards  that went  on the side slot (GVP made one, I recall). If you use any of  those try  to avoid putting anything on the CPU socket.
                     
 My goal is to setup an A500 for  running games off disk for my brother's kids.  I don't really want to  add anything else external onto the machine  through the CPU slot, but  rather keep it as simple as possible for its  5-7 year old endusers.  My  current config is stock Rev 6a with a single 512k expansion in the  trapdoor.  No Chip RAM mods or anything done to Angus/Gary.  I'm not  looking to run WHDload for the present, and I don't have any IDE/HD/CF  interfaces of any kind.  But I still think a little more RAM would be  helpful.

One fellow on Amibay has built a 2MB CPU piggyback plus IDE interface  board.  However, it has no auto-config support on the board itself and  always needs a bootdisk.  The other possibility I found was this 8MB CPU  piggyback card made by Elbox.  But 8MB Fast RAM is really beyond what I need for running disk based games:

http://www.buy.elbox.com/cgibin/shop?info=660E500

I haven't really even looked at doing anything with Chip RAM yet.  Any advice what route to take?
 

Offline hoptoitTopic starter

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Re: A500 CPU piggyback RAM not the best?
« Reply #1 on: October 15, 2010, 09:26:43 AM »
Not too much trouble to do it so I ordered some 256 DRAM DIPS from Nathan's shop to do the real 1 MB Chip RAM upgrade.  I will pull out the old 512k card afterwards.

I will keep an eye out for a good CPU piggyback expansion in the future in case I wanna get in to WHDload land.  It seems better than trapdoor options.

This project looks to be interesting if someday completed:
http://www.students.tut.fi/~leinone3/ram68k/

I wonder if the 16-bit RAM it plans to use a good match for the A500?  Does it make a big difference what RAM type goes through the CPU slot?