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| Metalguy66 A500+ | ||
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Description: A500+ *50mhz Derringer 030/882 w/ 32megs *custom plastic bracket to hold Derringer in CPU socket. *2megs chipram hard-wired on motherboard. *RTC battery replaced with CR2032 Picture Stats: Views: 3292 Filesize: 255.48kB Height: 768 Width: 1024 Posted by: Metalguy66 at October 13, 2008, 03:32:58 AM Image Linking Codes
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| rkauer Posts:3263 | March 26, 2009, 07:47:14 PM Only useful thing someone can toss on the A500/+ trapdoor is a 286 card. |
| Metalguy66 Posts:122 | March 09, 2009, 06:30:22 PM This derringer came from a Guy named Marshall Belew... It was in a rev 6a A500 when I got it.. This one was 50mhz from the factory.. I don't know what Derringer you are talking about, Martin.. Ive had several of them over the years, but this is the only one I have now.. And its the only one Ive ever owned that was a (true) 50mhz.. Did I get a Derringer from you? Admittedly, my memory sucks about what all AMIGAs Ive owned & where they all came from... |
| Methuselas Posts:2205 | March 08, 2009, 01:46:14 AM I miss that Derringer. =C You still using the same 32MB chip I had installed on there? |
| Metalguy66 Posts:122 | December 26, 2008, 07:45:55 AM A 1meg chipram (A501+, etc.) expansion hooked to the trapdoor slot would be "wired" exactly in paralell with the ram on the motherboard, and thus would be redundant. It would not show up as additional ram. Why did I put the extra meg on the motherboard? Because I had the chips laying around, I wanted 2 megs chipram, I realized how easy it would be to do, and I did not want to pay for a 1 meg expansion board (they are very rare in the U.S.) |
| sim085 Posts:958 
| December 24, 2008, 02:50:49 PM Hi, Sorry for taking so long to reply back. Thanks for the information. I never knew that fast ram could be added in that manner. On my A500+ I have a 1MB chipram expansion board and a GVP A500 HD8+ with 4MB of fast ram on it ... However I was more interested in knowing what would happen to your A500+ if you connected a 1MB chipram expansion board to it now that you did that fix? What chipram would be used? The one on the motherboard or the one on the expansion board? Also (and this may be a personal question :-P), what inspired you to do this fix? |
| Metalguy66 Posts:122 | December 19, 2008, 05:49:29 AM you dont.. In fact you wouldnt WANT to put any ram on that slow-assed bus.. The only thing the trapdoor is good for on ANY A500 is chipram and clocks.. Any fastram you put on there will have slow as hell CPU access every time agnus decides to hog the chip bus. Many people refer to this as "slow ram".. This is why memory expansions like the Adram5x0 suck as fastram expansions. True "fastram" needs to be on the CPU or Zorro Expansion bus.. If you have an acclelerator, the 32-bit fastram that they use is even better, although it cant alwayse be mapped into normal "fastram" adress range without interfering with things like DMA from zorro devices.. This is why I have 8 megs of true "fastram" on the zorro bus, as well as 32megs of 32-bit fastram on the accelerator. disabling the accellerator makes it a "stock A500" with 8megs fast & 2megs chip... |
| sim085 Posts:958
| December 12, 2008, 07:51:37 AM First of all congrats on your mod ... it looks really nice. I had a question however; what do you need the trapdoor slot for now that you already have 2MB chip ram on your motherboard? |
| Metalguy66 Posts:122 | November 11, 2008, 07:31:56 PM The Mod you see only works on a rev 8a (A500+) motherboard. Just piggyback 8 more 256k x 4 DRAMs on top of the existing ones. Bend up pin 17 of all 8 of them. Hook all of the bent up pin 17s from the left 4 chips to pin 11 of U32, and hooke all of the bent up pin 17s from the right 4 chips to pin 5 of U32. Explanation: This is accomplishing the exact same thing as plugging an A501+ (1meg) ram expansion into the trap door slot. U32 is a 74LS139 DEMUX. It takes the two CAS signals from agnus, and demuxes them based on the state of _DRA9, creating 4 separate CAS signals. two are hard wired to the existing moterboard DRAM, and the two extra ones are available at pins 5 and 11 of U32 (also at pins 35 and 36 of the trap-door expansion connector). Since all the other signals (adress, data, RAS, WE, etc.) are common between the motherboard ram and the trap-door slot, you just need the two additional CAS signals, and you can just piggyback the DRAM chips to get everything else. For 2 megs ChipRAM on A500 Rev. 6a See this thread: http://www.amiga.org/forums/showthread.php?t=38607 I havent tried it yet, but this basically turns your Rev 6a into a Rev 8a with 2 megs chip. You do need an actual A3000 AGNUS chip though. |
| czarek Posts:74
| October 17, 2008, 12:36:57 PM Hey I'd like some info about that mod. How do you do that? Is it just replacing memory chips to bigger ones or something else? I see some wiring between modules and U32, what is that? |
| BuzzBrain Posts:133
| October 14, 2008, 12:58:42 PM Nice a500+  I like your "mod" to held the derringer board in place. Think I'm going too copy it. |
| motorollin Posts:8669 | October 13, 2008, 07:15:33 PM Glue on an AGA chipset and you've got an A1200 ;-) -- moto |
| darksun9210 Posts:1317 | October 13, 2008, 02:05:09 PM that rocks! how have you done the chipram mod? oh wait-a-sec, is that a rev6/8 board? darn. i don't suppose its possible to butcher 2Mb of chipram onto a rev5 board :lol: |
| derringer3 Posts:368 | October 13, 2008, 08:59:54 AM awesome! |