2 mb chip ram for A600

[DrF]

So has anyone worked out what happens to the trapdoor expanstion slot after this mod?

I would assume that either by putting a A601 or silmiler in there, the A600 would either not see it and carry on, or not work?

Now if there was a way of getting more fast ram without paying a sh*t load of cash

[alexh]

I personally think you might get a fire.

Two chips driving the same wire? No thank you.

For A600 FastRAM you just buy one from LordV and assemble it yourself.

[Jope]

It will conflict.. Most probably the machine will just crash when you access the second megabyte of chip RAM.

[Merlin]

@ alexh

I would have thought you were more at risk of a fire from sticking an Apollo into your A600.

Just how much current at 3.3v are you expecting to draw down the wires feeding two ram chips, in order to cause a fire? If your argument held any water, adding extra ram chips to the main board of an A500 should also cause the same effect, would it not?

M

[Merlin]

@ DrF

The trapdoor is basically redundant after this mod, as the 8375 Agnus can only address 2Mb of chip ram. More than 2Mb of chip ram on the A600 requires a DRAM controller as per Lord Vader's mod, in order to address the memory above the standard 2Mb.

That is why Lord Vader needs the CPLD device.

M

[Jope]

More than 2MB of chip RAM requires a redesign of the Agnus.

[Merlin]

^^^ What Jope said as well ^^^

M

[alexh]

Originally Posted by Merlin

Just how much current at 3.3v are you expecting to draw down the wires feeding two ram chips, in order to cause a fire? If your argument held any water, adding extra ram chips to the main board of an A500 should also cause the same effect, would it not?

No. How can I explain it in a "Dummies guide to hardware" style?

When you add extra RAM to an Amiga, normally you add the RAM to unique addresses. No RAM occupies the same address as other RAM.

If you solder in RAM to your A600 in the 2Mbyte chip RANGE ($080000-$1FFFFF) and then also add an A601 (trapdoor) expansion (also at $080000-$1FFFFF) you are adding them in parallel.

A read comes in and BOTH chips try to drive the data bus (wires) at the same time!

[Merlin]

Fair enough-ski, I read your post in the electrical sense, not the data sense.

Anyone who tries this mod is taking a risk anyway.

M

[Jope]

That might lead to fried drivers in the chips, but are you serious that there's enough current flowing there to burn traces off the board? It's just signals after all.

[coze]

Originally Posted by Jope

More than 2MB of chip RAM requires a redesign of the Agnus.

also, the denise, paula (basicly all chips which will acess it), and a redesign of the memory map, whole adress bus and probably changes to kickstart.

so actually it requires a new ECS design

[DrF]

I know theres a 2Mb chip ram limit, I was thinking like this VERY old A500 I have where if I added a 1Mb trapdoor expanstion (A501+ I think it was) it would give me 1Mb fast and leave the orig. chip ram alone, the same expanstion on a A500+ gave me 2Mb chip ram, I went on about it in another thread, not so long ago, why it did this no one could work out, but there ya go

[Charlie]

Hacking - good.
Clockport - better?

Don't discount AK's upgrade. That little clockport header could make all the difference to a project...
...but what if you want to use the expansion port for something else..?
...back to hacking...
...but will the expansion port be useable for anything after this hack..?

...my brain hurts...

[alexh]

Originally Posted by DrF

I added a 1Mb trapdoor expanstion (A501+ I think it was) it would give me 1Mb fast and leave the orig. chip ram alone, the same expanstion on a A500+ gave me 2Mb chip ram, I went on about it in another thread, not so long ago, why it did this no one could work out, but there ya go

The A500+ has an 8375 2Mbyte Agnus regular A500's have either an 8371 512Kbyte Agnus or an 8372 1Mbyte Agnus.

Adding an an A501+ to a regular A500 (if it works) would probably only give 512Kbyte Fast RAM.

[rkauer]

If someone want to make his own "A601", without RTC, nor clockport, I've uploaded one to Aminet:
http://aminet.net/docs/hard/Tabajara.zip

It is in html form, so any computer can read it. The instructions are in english and brazilian portuguese.

[Merlin]

@ Charlie

In a word, NO. The expansion port can't be used for data after this hack as the Agnus is at it's 2Mb limit.

@ DrF

You haven't got an A501+ 1Mb upgrade going spare, have you? (Hint hint)

M

[Toni Wilen]

Originally Posted by coze

also, the denise, paula (basicly all chips which will acess it), and a redesign of the memory map, whole adress bus and probably changes to kickstart.

so actually it requires a new ECS design

Original Denise and Paula will be compatible. All DMA address pointers are in Agnus. (Agnus fetches the data using DMA and then writes it to Paula/Denise xxxDAT registers)

[Merlin]

@ rkauer

I started to work out the pinouts for your project from the tables listed and I needed coffee and paracetamol after 10 minutes, to be honest it was easier for me to translate the German hack described above (lazy git that I am LOL).

Edit: Anyone for a schematic? Courtesy of Zetr0 and yours truly, credit to Ralf at a1.org for the hack.



M

[Merlin]

For those who may be interested, I nabbed two S3 Trio 2Mb graphics cards with compatible chips from Fleabay for £8 all in, that's enough chips to mod four A600s. Cirrus Logic cards seem to be going for similar prices.

Go get 'em lads!!

Merlin

[Hungry Horace]

i love the fact that in this thread from only a few months back "1mb chip ram expansions are dead cheap" and "you can easily get one from amigakit"

4 months and things have changed that much? all i see is "Out of Stock" on every a600 chip expansion on any amiga shop, and massively inflated e-bay prices.

if i have compatible chips, i've very tempted to try this.