a500 rev 5 1mb chipmem mod... confused
 

Hi All,

Can someone explain this, i am confused...

according to all i have seen, the Rev 5 mobo requires jp2 cut and the upper 2 pads blobbed, and also a trace cut near the expansion port. It also apparently requires a Agnus 8372A to allow 1 mb of chipmem. here is a picture of the Rev 5 motherboard i have done and it reports 1mb chipmem and the 2.05 kickstart only needs 1 wire and not 2 ?

I cut the trace between the lower 2 pads of JP2 and blobbed the upper 2 pads of jp2. added 1 wire to KS2.05 from pin 1 to pin 31. I cut no other traces or lifted any pins out of sockets. I used my own fastmem board and removed the blob on my expansion board from the _extick jumper (pin 32). I left the agnus 8371 onboard and booted up... here is the results...

http://www.kipper2k.com/a500/rev51mbmobo_small.jpg

(one important thing to note, a lot of fastmem expansion boards have pin 32 set to ground so you may have to cut a trace on the motherboard that feeds pin 32 of the fastmem board.

here is what avail reports

http://www.kipper2k.com/a500/rev51mbavail.jpg


here is the supersized motherboard picture.

according to wiki, i should not get 1mb chpmem.

http://en.wikipedia.org/wiki/MOS_Technology_Agnus

Two wires + the bent leg are only needed if you use an EPROM based ROM chip (all 3.1 chips are EPROMs). The mask ROMs are always in 16bit mode, so only the address line needs to be moved to the right pin with one jumper.

The 1MB chip mod is as you described for the rev 5.

You can also bend out the _extick/_exram pin from gary if your slow mem board doesn't have a switch and you don't want to cut the trace. (edit: no, don't do this)

Indeed you shouldn't. Now is a good time to fill all of that RAM with lha packages and then run lha t against them. :-)

Very curious. I seem to remember you were supposed to get green screens or "yellow gurus" if you do this with the 8371.

Oh yes and try to set a large screenmode, get some of that upper chip ram into use.

Thanks for the info Jope, I done a couple of tests on the board and the ram is real, i was able to copy files to and from upper chipmem area and was also able to play superfrog on WHDload which requires 1mb chipmem. I did find an article that was written by Zetro done a while back that states that the 8371 does support 1mb chipmem. it appears that this is the cas so far.

I did same thing on one board and it worked (it was real chip ram , played mods , opened screens etc).

Reason I did it was I didn't have 0.5 mem expansion at hand :P

Maybe someone could confirm what are limitations of of rev 5 (I'm guessing that in can address 1 Mb as CHIP or 0.5 CHIP 0.5 Slow).

I used this :

http://aminet.net/package/docs/hard/1MBChip

No sorry , that's not it , I can't find it now.
From what I remember I soldered memory chips added components cut the trace and that was it.

I think I remember reading that doing so meant you can no longer use trap door extension but not sure.Motherboard was not v6 and it had kick 1.2 by default.

Hi kipper, so just to clarify, if I have a Rev 5 with KS 3.1, and already have 8372A Agnus, all I have to do is:

- Cut lower part of JP2
- Place a solder blob on upper part of JP2 just like your photo
- Remove the blob on your expansion board from the _extick jumper (pin 32)

That's it?

indeed a 8372a is required for 1 mb chip.. did you confirm that dma actually works for the upper half meg of chip? because with an agnus not supporting 1mb chip, i think it is accessible for the cpu, but not dma..

It's as if some messages are missing from this thread? I seem to remember we determined that it will not really work even though the OS sees 1MB chip.

I think that was a different thread about the Rev 6A?

Could be. My memory isn't what it used to be. :-/

Nevertheless: the 8371 will not do 1MB chip, even though it appears to work. :-)

Much better 1M chip test: set WB to 1 plane mode, reboot, run programs/fill RAM disk until you have about 300k or so chip RAM left. Set WB to 3/4 plane mode. Corrupted display = upper 512k is not true chip ram.

With wrong Agnus, or with every chip mod no matter which Agnus?

You get corruption with a 512k Agnus.

Is anyone able to confirm this? @kipper2k?

That's it. The extick can be disabled by any means you like.

Some trapdoor ram boards have a switch. Turn the switch off.
Some have a solder blob / jumper, desolder/cut the jumper.
If you don't have either, then the nicest non-destructive method is to remove GARY and bend out the extick/exram pin so that it doesn't go into the socket. (edit: no, don't do it, it needs a pullup resistor)

That sounds like the way to go. Do you have a link to a picture?

GIS for gary pinout, and this was one of the first hits:

http://megaburken.net/~patrik/pinout_temp/Gary.gif

OK, so I bent out Pin 32 like this:
http://www.jspusa.com/technical/jspfig1b.jpg

Still only 414K of graphics memory.

Do I also need to cut JP2? I just want to be clear about what you're saying before I do anything.

Yes, JP2 is very important here. Cut and solder to the other position.

OK I've done everything.

Whilst doing it, pin 31 of my Kickstart 3.1 became loose. Then the pin fell off the Kickstart completely. I've attempted a solder repair.

When turning on the A500 Rev 5, now I either get a copper colored screen or a yellow colored screen.

Copper used to happen and still does when the Kipper2k Fastmem with IDE board isn't secure. If I push down on that the yellow screen (a new thing) now happens.

I'm trying to work out:

- Is the copper or yellow screen due to the JP2 mods gone wrong somehow?
- Or is the copper or yellow screen due to the Kickstart pin 31 coming loose meaning my repair isn't making contact with the pin's nub (which is recessed inside the chip – nightmare)?

It is very possible that your pin 31 problem is the culprit, in case the ROM is in 8 bit mode.