Still confused 8375 Agnus

[AmigaPixel]

hi all
I am revisiting an earlier post by amigan24. I am still confused as hell. The Big Book of Amiga Hardware list all of the 8375 versions as 2mb. I have one I tested a few years ago and it was 1mb. It's some where in the house I'll try to find it for the numbers on it. BBoAh also list the Mega Chip but does not state whether or not it is DKB's Mega Chip. Is the same one? Also I was wondering which if any need to be modified like the DKB MegaChip and which do not? Thanks

Here is how it list the versions of the 8375:


Agnus (2MB)     8372AB     318069-03     A3000 (PAL), A3000T (PAL) (came after 8375B)
Agnus (2MB)    8372AB    318069-039    A3000 (NTSC)
Agnus (2MB)    8372B    318069-03    MegAChip (NTSC)
Agnus (2MB)    8375 R0    318069-18    A500+ (PAL), A600 (PAL)
Agnus (2MB)    8375    318069-10    A600 (PAL)
Agnus (2MB)    8375 R2    318069-10    A500+ (PAL), A600 (PAL)
Agnus (2MB)    8375    318069-11    A600 (NTSC), MegAChip (NTSC), Mini Megi Chip (NTSC)
Agnus (2MB)    8375 R2    318069-11    Mini Mega Chip (NTSC)
Agnus (2MB)    8375    318069-17    A500 (NTSC), A2000 (NTSC)
Agnus (2MB)    8375    318069-19    A3000 (NTSC), A3000T (NTSC)
Agnus (2MB)    8375    390544-01    A500+ (PAL), A600 (PAL)
Agnus (2MB)    8375    390544-02    A500+ (NTSC), A600 (NTSC)

[AmigaPixel]

I found this related posting from 2006, by Alex Holland basically asking the same thing but he points out errors in the table. Could anybody clear this up?

http://newsgroups.derkeiler.com/Archive/Comp/comp.sys.amiga.hardware/2006-02/msg00025.html

[AmigaPixel]

Correction it was barney who posted the orginal question.

[AmigaPixel]

@alexh Thanks for the link to the thread.

[AmigaPixel]

I going to open up my A2000 to see what the 8372A has for the rest of the numbers. My 8375 Agnus is at a different location, I hope I can get to it soon so I can check it out.

[AmigaPixel]

On the 2mb 8375 Agnus chips that are compatible for the A500/A2000, do they need any modification like the DKB Mega Chip does?

[AmigaPixel]

Ok, to make sure, which of the NTSC 8375 2mb Agnus chips are compatible with the A2000 and what are the full set of numbers?

thanks

[AmigaPixel]

@Zac67

 Thanks that helps to clear it up more, however I didn't think the A3000 needs an adapter? it already has 2mb chip ram right, unless some early models came with 1mb only.  I guess it means I will have to find a DKB MegaChip, or is there another brand?Thanks

[AmigaPixel]

@Zac67
 
Ok I found the answer to the my question on wether there were other chip adapters. They probably were not as common as the DKB brand I would imagine but I might be wrong. I do seem to recall seeing the DCE Mini mega chip advertised enough.

I do see now from BBOAH that some A3000 did come only with 1mb but ready to upgrade to 2mb chip. I should look these things up before I ask questions, even if they turn out to be partially wrong  sometimes.

[AmigaPixel]

Alright,
I think this all falling into place. Correct me if I am wrong (and you know you will!) The Fat Agnus is the DMA controller as well as other functions. It does not hold the actual chip ram but can address 512k, 1mb or 2mb depending on the chip revision.  Hence the need for an adapter on A2000 and A500, the adapter which has the 2mb chip ram on it along with the Agnus 8375 or the socket and the wiring to the Gary chip.

In regards to the A3000, the ones that came with only 1mb chip but had the expansion socket for 2mb, I assume then the Agnus had to be upgraded as well. if so did they require an adapter too or could the chips be plugged right in?

I love learning this stuff, even if it is 20 years later!

[AmigaPixel]

@alexh

Ooops! My bad, 1mb chip ram.

[AmigaPixel]

After a bit of research I found out that I wasn't completely wrong all this time (but not completely right either):
Some early A500+ actually used (old) A500 rev 7 mainboards (1 MB Agnus with 512 KB onboard) but apparently they got the '+' for the 2.04 ROM they featured. 'Real' A500+ have a 2 Meg Agnus and 1 MB onbard, of course.

Again BBoAH isn't too precise here, as it talks about 'OCS' and 'ECS' versions in that respect, neglecting that the 1 Meg Agnus is ECS already (OCS is 512 K chip and 512 K 'ranger').

Right, that makes sense. When I had my A500 it only came with 512k, but I was able to upgrade to 1mb with the A501 card or A501+ I can't remember which I had. So it Already had the 1mb Fat Agnus but mine came with AmigaDos 1.3. I guess it would have to since only had 512k installed. I wished I checked to see what rev mobo it had, 5 or 6.

[AmigaPixel]

- the one from A3000 - controls 2 MB chip RAM, A3000s had 1 MB chipmem out of the box, but are easily upgradable....

-That leaves the A500/2000 owners with the wish to upgrade to 2 MB chip. Here come the adapter boards (Mini Megi et al), allowing to fit an 2 MB-Agnus (A3k mostly) on a otherwise not suited mainboard. Which of the 2 MB chips they require depends on their design - the A3k Agnus was first, so it was favoured.

Yes but later A3000's came with 2mb chip already installed. In the those machines was the chip ram soldered onto the mobo or was it upgraded by plugging the extra 1mb into the available socket?

In regards to the Mini Megi and other adapter boards, I would think the 8375 work in those too.

[AmigaPixel]

@Zac67

Well I don't know, Do you know which adapters come with the Agnus chip already installed?