Amiga 500 - AdRAM 540

[blindguy]

Hello everyone, nice to meet you all.

I just received an Amiga 500 from eBay and had a few questions.
It appears to have a AdRAM 540 with all the chips filled in so I think it is 4MB but as they advertise only 2.5 MB RAM is autoconfigured, so I have to figure out the software to see all of it.
http://amiga.resource.cx/exp/adram5

The bigger question I have is about the subboard that sits ontop of the Gary and is sodered to the motherboard.

Looking at the Agnus chip it sez fat agnus on the board and 8372A  318069-02  5188 23 on the chip.


Also on the board it sez
 B52/Rock Lobster
GRR/JSP/GUAY/FISH
A500N
and I think it is a Rev 5 board but there is a sticker on it that I odn't want to remvove.

SO I think I have a Fatter Agnus due to the 8372A  on the chip.
The questions is think I can pull the current Agnes and put in t a Super-Fat Agnus chip without having to do more sodering?
Also, what is this PHOEBE Agnus chip board that the Gary sits on top of do?
Thanks for any assistance in advance!

[blindguy]

ok so I gtot he software going and here is what it sez:

          available  max

chip     969824   1047520
fast    3596592   3662552
total   4566416   4710072

that makes me thik I have a 1 meg ECS agnus
The question I have is can I swap it out with a 2 meg agnus?

Thanks for your thoughts and ideas

[zipper]

No, different pinouts on 1 and 2 Meg chips.

[blindguy]

Bummer, thanks for the prompt response.

[Motormouth]

The bigger question I have is about the subboard that sits ontop of the Gary and is sodered to the motherboard.

I have one of these in one of my A500

subboard probably for the Ad540

http://amiga.resource.cx/exp/adram540

It allow for more than 1 meg of ram to be mapped from the A500 trapdoor slot.

Two things to remember,  1), as you mentioned, the ram above the 2.5 megs needs a command (usually early in the startup-sequence) to mount it.
2),  The "fast" ram is not truly fast.  It is mounted in the "fast" ram memory space, but is limited to the trapdoor speed.
This is usually referred to as "slow-fast" ram.  So that it is not confused with true 16 bit "fast-fast" ram.
The amiga will be faster than an A500 without fast ram, but not quite as fast as an amiga with true fast ram.
ie relative speed:  slow ram < 16 bit fast ram (usually zorro II or 86 pin expansion) < zorro III 32 fast ram < 32 bit fast ram on motherboard or processor expansion board