25 May 2020, 22:23 | #1 |
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Amiga 500 memory upgrades
I have an Amiga 500 REV6A that has the trapdoor memory expansion. On the board itself, it says 512K/1M. It has four soldered RAM chips and four empty spaces. I assume for bumping the onboard memory to 1 MiB.
Now, if I did that, and used the trapdoor memory, how would the memory be arranged? Would it be 1 MiB of CHIP RAM and 1 MiB of FAST RAM? Or something else? Thanks |
26 May 2020, 01:49 | #2 | |
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The expansion RAM would still be only 512kB and (as far as I remember) would cease to work, because your A500 with 1MB chip mem basically behaves like an A500+. You could even fit it with an ECS Denise to enjoy the extra Screenmodes. The only thing that would be missing in comparison to a real A500+ would be the onboard clock circuitry. |
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26 May 2020, 02:26 | #3 | |
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No you dont need the Agnus form the A500+. it wont work in a rev 6 Amiga because of a different Pinout of the 8375 Agnus. the Normal Agnus for a REV 6 amiga (should be an8372A ) can handle up to 1 MB Chip. If you upgarde the a500 onboard you will have 1 MB Chip. For the jumper setting see here: http://eab.abime.net/showthread.php?t=88689 After modding a 512 KB extension will not work anymore. |
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26 May 2020, 03:34 | #4 |
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Ah, thanks for the clarification.
So, as it stands now...with 512K onboard and another 512K in the trapdoor, do I have 1MB of chip RAM now? I have four A500's total. Three of them are REV5 boards and this one is a REV6. Out of them, I'd like at least one of them to have maxed out chip RAM and maybe a little fast RAM. Thanks! |
26 May 2020, 06:59 | #5 | |
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So in my experience, the answser is... "no", you have 512K of Chip RAM and 512K of slow RAM. But other people may have figured out how to make the trap door RAM act like Chip RAM, in which case I'd be wrong. =) |
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26 May 2020, 07:19 | #6 | |
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If you toggle JP2 and cut JP7, you will get 1MB of chip (if no previous owner stole your 1MB Agnus and replaced it with a 512k one) |
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26 May 2020, 13:19 | #7 | ||
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Quote:
Quote:
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26 May 2020, 14:03 | #8 |
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I thought slow RAM was Chip RAM?
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26 May 2020, 14:37 | #9 |
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No, while it is true that ChipRAM is slow, SlowRAM is basically FastRAM... ;-)
Jokes aside, SlowRAM is just a sloppy word for something called Ranger Memory. It's the kind of special memory you can put in the trapdoor expansion of the A500 (or on the A2000's mainboard). While this kind of RAM is controlled and refreshed by the chipset, it is not ChipRAM per se (only if you set the aforementioned jumpers it can become ChipRAM). Because it's not controlled by the CPU directly, it is also not FastRAM, hence the term SlowRAM. And since the A500 chipset, i.e. Agnus, can only control a total of 1MB, this also explains why you can't use 1MB of ChipRAM AND 512kB of SlowRAM. |
27 May 2020, 02:05 | #10 | |
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Only the early Rev6 had a Agnus 8317.This Agnus can only adress 512 KB chip Ram so you had to replce it. But the most common Agnus in the Rev 6 is the 1 MB Agnus. |
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27 May 2020, 03:06 | #11 |
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Slow RAM is memory on the Chip RAM bus that the custom chipset can't access. You can't use it for sound/gfx etc. but since it's on the same bus as Chip RAM, the CPU still has to wait for cycles on the bus to use the memory (because the chipset is still using the bus to talk to Chip Memory). In the OS it shows up as "Fast Memory" but it's not true fast memory because it has all the same restrictions as Chip RAM. |
27 May 2020, 03:23 | #12 |
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I just confirmed my Agnus is the 8372. I also just ordered some more RAM for onboard. Of course, I forgot to order sockets. lol So that will be next.
After I add this, and do the jumper configs, I will have 1 MiB of CHIP RAM. At which point I will take the expander and use in another Amiga. Thanks guys for the information. |
27 May 2020, 11:39 | #13 |
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Just a heads up, you might want to source ultra-flat sockets because it gets tight with keyboard clearance once you put standard 20 pin dip sockets in there. Check out the (sticky) thread "Amiga 500 mod to Amiga 500+" in the Hardware mods section, I added some pics a while back in the end of that thread.
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27 May 2020, 16:31 | #14 |
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Good idea. I didn't think of that. I actually found some sockets I had that are 20 pin (dual wipe). I then searched for low profile sockets and they honestly look the same size as what I got. Didn't seem any shorter than normal.
Do you have any recommendations or know where I can find some? I also have some machine headers that might be lower. Thanks |
28 May 2020, 04:49 | #15 |
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Well, you were correct. I put a standard socket in there with a chip and the keyboard definitely was pressing down on the chip.
Fortunately, I found some ultra-low profile sockets pretty cheap so they should be here soon. Thanks! |
28 May 2020, 11:11 | #16 |
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No Problem. Glad it helped. With a Rev 6A motherboard I would rather use the trapdoor expansion port though, and not populate the four empty slots on mobo. Most memory expansion cards has a RTC chip (real-time clock) onboard which is useful if you prefer to have correct timestamp on files created/modified in wb. Anyway, socketing the DRAMs makes them easily removable should you change your mind later on.
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