add 1 MB onboard ram to A500 Revision 6A MB

[Tenacious]

@klx300r

You have 1 Meg of chip ram, right? Not 512K of chip and 512k of fast when the sidecars are all pulled off, right?

[klx300r]

Tenacious wrote:
It would be interesting if rkauer's link will convert a NTSC A500 into a defacto A500+ (I came away from the link a little in doubt).  If it works, (and you have 2-Meg Agnus) then all you need is a European (1 meg) A501 mapped to the chip memory address space.

The mod I mentioned above puts all 2 megs on the motherboard, the A501 is retained for the RTC only and its memory is disabled.

The Aminet links are broken because the directory structure was consolidated.  The hardware hacks were moved under the docs.  aminet.net/docs/hard/A2K_agnus_hack.lha

Good Luck

ok thanks i'll check it out but I have a 8372A Agnus which is only 1 MB..i beleive the 8375 was 2 MB but im not sure

[klx300r]

Tenacious wrote:
@klx300r

You have 1 Meg of chip ram, right? Not 512K of chip and 512k of fast when the sidecars are all pulled off, right?

well right now without my sidecars I have 512 chip 512 fast but hopefully this mod will give me 1mb chip and  if I can still keep my RTK that would be great too :-D

[Damion]

Tenacious wrote:

You probably know this, but Supra's 500 RX fast ram expansion is one of the best first moves you can make (if you're not going for a HD/ram combo).   I wish I had had one of these back in 1989!

I'll never forget the day I got my Supra 500RX. Next to my HS girlfriend, it was almost more excitement than a kid my age could handle. ;-) Good times indeed! :pint:

[Zac67]

If you want to have 1 MB chip, the first thing you need is that your Agnus has to be able to handle it. Whether the 2nd 512K sits on an A501 or onboard does not matter a single bit.

With a 1 MB Agnus, you just change the A19 jumper and open the _EXRAM jumper, that's it.

[klx300r]

Zac67 wrote:
If you want to have 1 MB chip, the first thing you need is that your Agnus has to be able to handle it. Whether the 2nd 512K sits on an A501 or onboard does not matter a single bit.

With a 1 MB Agnus, you just change the A19 jumper and open the _EXRAM jumper, that's it.

whoooaaaaa  :-o ok (me shuts off soldering iron for now) now since I already have the 256 drams can I install them on the mb without any conflict  :-?

[Tenacious]

@klx300r

I caught on too late, sorry.  The A500 technically has 3 kinds of memory, but, only 2 labels to call them by.  Pretty confusing, huh?

Chip Ram:  memory that is shared by the CPU AND all of the coprocessors.  This memory is managed by the Agnus chip.  The CPU must waite for its turn to use it.  The A500s (not A500+) all shipped with 512K of chip memory on the MB.

Fast (slow) Ram:  This originally was the memory on the A501.  Commodore mapped this memory to a different block address than the 2 Meg address space reserved for Chip.  It is not shared with the coprocessors, however, it is still managed by the Agnus chip.  The CPU must wait to use it as well.  This address space is called Fast by Commodore, but it's not true fast nor true chip. This address range has worst attributes of both kinds and should not be used.

Fast (true) Ram:  This memory comes off the side CPU connector and is never shared or slowed by the coprocessors.  It comes with its own refresh circuitry (not managed by Agnus) and so the CPU can run full speed through these addresses.  8 megs is the max. for the stock 68000.

This strange situation came about because of the evolution of the Agnus chip, which could originally address only 512K
of memory (used in A1000 and, I think, some A500s). The next version could address 1 Meg of chip, used in most A500s and A2000s.  The Super Agnus could address 2 megs and was used in A500+, A600, A3000, etc.

Commodore provided jumpers on later A500 MBs to select the address range where the A501 could live, but, set it to Fast/Slow by default.  Really stupid.  There are several docs on Aminet that detail moving the A501 to the true chip ram address range.  Probably, most A500s that remain have had this simple modification.  I'm surprised that yours didn't.

As a practical matter, 1 Meg of chip is usually enough for an A500, 3 of my A500s are configured this way.  Without a 2 Meg Agnus, I don't know how you can utilize the extra chips you bought.  Maybe someone else does.

I'm gonna sign off, I'm missing "Polar Express" with the kids.

[Zac67]

Without somewhat severe modifications to the board, esp. Gary's address decoding logic, you can't use more than 1 MB chip/'fast' total.
There have been lots of boards that used a Gary adapter to actually multiply the slow-fast RAM to up to 1.8 MB, but they'd have to be made to allow 1 MB chip, else you'd also have to heavily modify them.

You should note that the 2 MB Agnuses in A500+/A600 and A3000 are essentially different in pinout as the latter can provide a 32 bit data path to chip RAM.

[klx300r]

Chain wrote:
http://eab.abime.net/showthread.php?t=31816

followed this thread and I'm more confused now then when I started out :-?  so did you ever get this mod to work to get 1MB chip soldered on board, 512k fast with RTC working fine on trap door on the Rev6A motherboard :-?

[Zac67]

Zac67 wrote:
Without somewhat severe modifications to the board, esp. Gary's address decoding logic, you can't use more than 1 MB chip/'fast' total.

Third try to explain:
You can't use the 2nd onboard 512K and the trapdoor RAM simultaneously unless you rework the addressing logic. If you don't understand what this is about, you won't be able to do it.

[klx300r]

Zac67 wrote:

Zac67 wrote:
Without somewhat severe modifications to the board, esp. Gary's address decoding logic, you can't use more than 1 MB chip/'fast' total.

Third try to explain:
You can't use the 2nd onboard 512K and the trapdoor RAM simultaneously unless you rework the addressing logic. If you don't understand what this is about, you won't be able to do it.

hey thanks for your help but I'm reading 10 different solutions from 20 different people worldwide :-?  so I guess now the safest bet is just to keep my trapdoor expansion slot and change a few jumpers to get 1MB chip I guess..i got enough fast ram with my supraram500rx and a590 anyhow :-)

say I already sucked the solder outta all the dram motherboard locations....is it safe to leave them open or do I have to resolder them closed??

[klx300r]

Zac67 wrote:
If you want to have 1 MB chip, the first thing you need is that your Agnus has to be able to handle it. Whether the 2nd 512K sits on an A501 or onboard does not matter a single bit.

With a 1 MB Agnus, you just change the A19 jumper and open the _EXRAM jumper, that's it.

change the A19 jumper to where :-?

[Tenacious]

@ klx300r

Most of us have been telling you the same thing. An ECS (or OCS) Amiga isn't likely to need more than 1 Meg of chip for any 1 application. I don't recall ever running out.  Going beyond the limits of your Agnus will require great knowledge on your part and the return on your investment deminishes very quickly after you acheive 1 Meg of chip.

What Jumpers?

Do you have access to Aminet?  There are a number files in Aminet/docs/hard/ describing the mod.  Get them all and decide which matches your MB revision, version of Agnus, and your sense of doing it 'right'.

You sucked the solder out of the MB?

Certainly, solder the chips back in.  Try to alternate between chips to prevent overheating any one of them.

Good Luck!

[klx300r]

Tenacious wrote:
@ klx300r

You sucked the solder out of the MB?

Certainly, solder the chips back in.  Try to alternate between chips to prevent overheating any one of them.

Good Luck!

ya i initially was gonna solder 4 new 256 drams into the empty sockets on the 6a mb but now i'm gonna go on the safe route and just leave my 512 trap door expansion in and allocate that to chip ram so that i get a 1mb chip ram total an hopefully keep my RTC working...my supram500rx and a590 will take care of the fast ram.

saying that I understand I have to open jumper 7A and do something else to jumper 2..(can anyone confirm what I must do to jumper 2 please...i checked aminet with no concrete answers there...thanks for the help :pint:

[Tenacious]

I checked Aminet and found the following files:

http://us2.aminet.net/docs/hard/A5001MChip.lha
http://de5.aminet.net/docs/hard/a500chip.lha

All talk about the Rev 6 MB and give a lot of detail.  There are even ascii diagrams of the jumpers.

To answer your question:

1. Remove the jumper (trace) between the middle and bottom pads of JP7.

2. Remove the trace between the middle and bottom pads of JP2 AND bridge a wire between the middle and top pads of that same JP2.

Look the files over.  There is another file in the same directory, 500Hacks, I think.  It details this and other modifications with switches so you can boot into Pal or NTSC.

Good Luck again!  

[klx300r]

EXCELLENT :-D  Just finished the mod and it worked great !!! got a bit of a scare when I first booted it up & got greeted by a green screen but I troubleshooted the problem as being some extra flux on the board sooo after a good cleaning all was fine and peace was restored back in my Amiga land :lol:

thanks very much for your help :pint: