2mb Agnus... ECS Amigas, chip hacks... what tha?!

abraXXious

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Now I am confused.

I always thought that ECS Amigas, with the exception of the A3000, only had a 1mb Agnus, with ECS Denise....

Now Im getting conflicting information. From one source I am being told that a 2mb Agnus will NOT work in an A2000 or A500 unless either installed in a 2mb chip board, such as the Megachip or Chip X etc, OR if it is one of the later revision boards with 8 ram chips (instead of 16) on the MB, then a 2mb agnus can be installed DIRECTLY into the agnus socket as long as a hack that replaces the mb ram (with double capacity chips) and a few other alterations are made.

But WITHOUT either the board or the hack, the 2mb agnus will not function at all, not even as a 1mb agnus returning amb of chip on boot up.

But then, another learned fellow tells me that thats "bollocks!" and rev 6.3+ a2ks and later revision a500s actually came with a 2mb agnus installed which only reports 1mb chip until the above mentioned hack is carried out.

Can someone shed some light on this? I have a revision 6.4 A2k and a 2mb agnus... can the agnus be installed directly to the mb? If so, without the hack will the machine boot (with only 1mb chip of course)? Will the (reasonably simple) hack work?
 

rkauer

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Put it on simpler words: any Amiga equipped with a socketed & square Agnus can use a MiniMegiChip/MegaChip if it doesn't have a 8375 Agnus already.

The A500 that can be upgraded to 2Mb chip RAM DIRECTLY, just adding more memory chips, are only the A500 rev8A/8A1.

The A2000 can't have more than 1Mb DIRECTLY (just soldering more memory chips), doesn't matter the board revision. Installing a MiniMegiChip/MegaChip is the only way.
 

Lugosi

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Well, there are the mentioned hacks that usually include adjusting the Agnus socket to the pinout of the (to be used) 2MB-Agnus, and adding/changing RAM-chips, like this here for example.

In this case though, the board is a rev. 6.4 - and those already came with an 8375 Agnus (a 1MB-version).

Now, if all versions of the 8375 Agnus had the same pinout (do they?), a 2MB 8375 should theoretically work "straight out of the box" in this board too, but unless the onboard RAM was also "adjusted", there wouldn't be any benefit to this - it would still only have the stock 1MB to work with.
 

AndyLandy

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There are a multitude of different Agnus revisions, so approximately everything you've said above is true.

The 1MB-max 'Half-ECS' Agnus is part 8372A and features in r6 A500s and r6.0 -- r6.2 A2000s.

The 8372B is a full-ECS 2MB part that is found in A3000s. I believe it's a drop-in replacement for the 8372A. It may be what's on the r6.3+ A2000s. I'd have to check with someone who has such a model. (Alas, mine's only a r6.2)

The A500+ came with an 8375 Agnus, which helpfully is wired completely differently to the 8372 parts. Stupid! But that was C= for you. I've no idea what the A600 has in it. I've heard rumours that it's pin-compatible with the 8372 range, but nothing conclusive.

Does that help explain things?
 

abraXXious

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Well, that was kinda' my point - so with this reasonably simple hack, you can have 2mb chip on an a2k without a dodgy chip ram board that crashes your system every time a mouse farts within a 5 mile radius?
 

abraXXious

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Okiez, well this rather simple hack requires a rev 6.3+ A2k - check, my system is a 6.4...

It then requires an Agnus chip, but it is asking for either an 8372B or 8375B... which is rather odd becuase one source says the 8372B is a 32 bit 2mb Agnus for the A3k!

Anywho, part number 318069-03 is an ntsc Agnus. I of course have a 318069-10 agnus which is the pal counterpart.

From what I have read they are both pin compatible...

... but since the hack is being done to an NTSC Amiga with an NTSC Agnus.... will it work being done to a Pal Amiga with a Pal agnus?
 

AndyLandy

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Okiez, well this rather simple hack requires a rev 6.3+ A2k - check, my system is a 6.4...

It then requires an Agnus chip, but it is asking for either an 8372B or 8375B... which is rather odd becuase one source says the 8372B is a 32 bit 2mb Agnus for the A3k!

Anywho, part number 318069-03 is an ntsc Agnus. I of course have a 318069-10 agnus which is the pal counterpart.

From what I have read they are both pin compatible...

... but since the hack is being done to an NTSC Amiga with an NTSC Agnus.... will it work being done to a Pal Amiga with a Pal agnus?

What's the Agnus part you've got in your r6.4 at the moment?
 

AndyLandy

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Well, that was kinda' my point - so with this reasonably simple hack, you can have 2mb chip on an a2k without a dodgy chip ram board that crashes your system every time a mouse farts within a 5 mile radius?

Technically, all the MiniMegi or other ChipRAM expansion board is doing is exactly the same as that hack, but the second MB of ChipRAM is on the expansion board, rather than the motherboard.
 

abraXXious

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My a2k HAD a 8372 agnus (1 Mb ECS) on board. I have removed the 2mb agnus, 8375 from an echotronics 2mb chip ram board (which is playing up, but I dont think its the agnus chip at fault) and was going to install that in place of the 8372.

That a2k MB is a pal system, and so are both agnus chips.
 

AndyLandy

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My a2k HAD a 8372 agnus (1 Mb ECS) on board. I have removed the 2mb agnus, 8375 from an echotronics 2mb chip ram board (which is playing up, but I dont think its the agnus chip at fault) and was going to install that in place of the 8372.

That a2k MB is a pal system, and so are both agnus chips.

Best check that'll definitely work first of all. Grab a multimeter on continuity mode and check that the pins on the socket are the same as on the connector on the other side.

I'm surprised that something as late as an r6.4 still only has a 1MB Agnus. I wonder if any A2000s came with a full-ECS Agnus. I'm not convinced they did.
 

Lugosi

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I'm surprised that something as late as an r6.4 still only has a 1MB Agnus. I wonder if any A2000s came with a full-ECS Agnus. I'm not convinced they did.

I'm surprised about that too, especially since it's said here in the description of J102:
Rev 6.4 motherboards and possibly later revisions come with an 8375 Agnus by default which does not support switching. It was made in in separate versions for PAL and NTSC

Also, if you look at the picture labeled A2000 Revision 6.4 Motherboard, Closeup (Bottom Right), it shows an Agnus 8375 (318069-17) on the board.
 

abraXXious

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Im double checking what the original agnus was in this MB, but I am reasonably sure it is only a 1mb agnus.

Supposedly, all 8375 agnus are pin compatible. So what would happen if you used an NTSC agnus in a pal system or vice versa?

Also, what would happen if the above mentioned hack was carried out using the 318069 - 17 agnus, assuming I have one?

My brain hurts.

Surely the 2mb agnus hack has been performed/documented on a Pal A2k?! I can only find reference to a single version of the hack (the one I mention above) and it assumes you are running an NTSC machine - but does not even SAY this, I only figured this out by looking up the agnus part number, which is an ntsc agnus.

If anyone has a url etc for a pal version of the hack it would be greatly appreciated.
 

rkauer

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Zetr0 have all the knowledge about the Agnus (Agnii?) pinouts you can imagine, but I know for sure that 2Mb Agnus versions have totally different pinouts compared to old 8370/8371/8372A (and 1Mb 8375, of course).

Because of this, you can't drop-in a 2Mb Agnus in an old board, it will not work at all and may fry both the board and the Agnus.
 

Zetr0

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@abraxy,

In a nut shell what makes an ECS chipset is infact the ECS DENISE as the A500+ is just a 2MB ECS machine, as is the A600, the A3000.

You can upgrade any A500 with an ECS DENISE and this will make it a 1MB ECS chipset Amiga.

now.... to get an A500 upto 2MB of precious CHIP RAM is not an easy task - you will need to modify the motherboard and in some A500 revsions quite extensively.

So lets talk Agnii for a moment

Agnus is the Amiga's Address GeNerator Unit (i forget what the s is for lol)

8370 / 8371 and 8372A are all 1MB agnus -
these are pin and signal compatible with each other.

8372B / 8372AB are 2MB Agnii that are found on the A3000

Interstingly the 8372B is both electrically pin and signal compatible with the 8370 and 8371 sockets and signals - and this would be the Agnus to us if you were to modify the A500 motherboard - more on that later


now there are a few more Agnii

8375 comes primarlly in three flavours
8375: 318069-16(or 17 ntcs) is a special 1MB Agnus that is pin / signal compatible with the original 8370/8371 and 8372 Agnus Sockets


8375: 318069-02(or 03 ntsc) is a 2MB Agnus found on the A600 - although its electrically pin compatible with the 8370/8371 and 8372 Agnus Sockets its not 100% signal compatible as some signals are ignored - thus braking the compatability with these machines - there are ways to generate the missing signals of course.


8375:3180544-xx is a 2MB Agnus that was only released for the A500+
the 8375:3180544-xx is NOT electrically pin compatible with the 8370/8371 and 8372 sockets. This Agnus has all the signals needed just not in the right order of pins - thus making it next to impossible to hack an A500 motherboard.


The better method would be to build a small PCB board and socket plug - re-arange the signals in the proper 8370 series socket and then the tricky bit of MUX'ing pin 58 (RAS1) and GARY - thus giving you 2MB of CHIP

heres some research notes I compiled on EAB with the help of a very knowledgable fellow on the subject

Zetr0 on EAB said:
@alexh

indeed.... the plot thickens more, heres some more research

Code:
[B]                8375            8372             8372B          8370[/B]
              [390544-01]     [A3000]
pin#        #desc           #desc        #desc        #desc

01        DRD13        DRD13        DRD13        RD13
02        DRD12        DRD12        DRD12        RD12
03        DRD11        DRD11        DRD11        RD11
04        DRD10        DRD10        DRD10        RD10
05        DRD09        DRD09        DRD09        RD09
06        DRD08        DRD08        DRD08        RD08
07        DRD07        DRD07        DRD07        RD07
08        DRD06        DRD06        DRD06        RD06
09        DRD05        DRD05        DRD05        RD05
10        DRD04        DRD04        DRD04        RD04
11        DRD03        DRD03        DRD03        RD03
12        DRD02        DRD02        DRD02        RD02
13        DRD01        DRD01        DRD01        RD01
14        DRD00        DRD00        DRD00        RD00
15                +5V        VCC        VCC
16        _RESET        _RESET        _RESET        _RESET
17        _INTR        _INTR        _INTR        _INT3
18        DMAL        _DMAL        _DMAL        _DMAL
19        _BLISS        _BLISS        _BLS        _BLS
20        _BLIT        _BLIT        _BLIT        _DBR
21        _WE        _WE        _WE        _RRW
22        _RW        _RW        _RW        _PRW
23        _REGEN        _REGEN        _REGEN        _RGEN
24        _AS        _AS        _AS        _AS
25        _RAMEN        _RAMEN        _RAMEN        _RAMEN
26        RGA8        RGA8        RGA8        RGA8
27        RGA7        RGA7        RGA7        RGA7
28        RGA6        RGA6        RGA6        RGA6
29        RGA5        RGA5        RGA5        RGA5
30        RGA4        RGA4        RGA4        RGA4
31        RGA3        RGA3        RGA3        RGA3
32        RGA2        RGA2        RGA2        RGA2
33        RGA1        RGA1        RGA1        RGA1
34        28MHZ        28MHZ        28MHZ        28MHZ
35        A20        A20        A20        _XCLK (,A20)
36        _CDAC        _XCLKEN        NC        _XCLKEN
37        7MHZ        _CDAC        _CDAC        _CDAC
38        CCKQ        _7MHZ        _7MHZ        _7MHZ
39        CCK        _CCKQ        _CCKQ        _CCKQ
40        14MHZ        CCK        _CCK        _CCK
41                TEST        PAL/NTSC    TEST    
42        CRA0        VSS1        VSS        VSS
43        CRA1        DRA0        DRA0        MA0
44        CRA2        DRA1        DRA1        MA1
45        CRA3        DRA2        DRA2        MA2
46        CRA4        DRA3        DRA3        MA3
47        CRA5        DRA4        DRA4        MA4
48        CRA6        DRA5        DRA5        MA5
49        CRA7        DRA6        DRA6        MA6
50        CRA8        DRA7        DRA7        MA7
51        _LDS        DRA8        DRA8        MA8
52        _UDS        _LDS        _LDS        _LDS
53        _CASL        _UDS        _UDS        _UDS
54        _CASU        _CASL        _CASL        _CASL
55        CRA9        _CASU        _CASU        _CASU
56                DRA9        DRA9        _RAS1
57        _RAS0        _RAS        _RAS        _RAS0
58        _RAS1        VSS2        VSS        VSS
59        A19        A19        A19        A19
60        A01        A01        A01        A01
61        A02        A02        A02        A02
62        A03        A03        A03        A03
63        A04        A04        A04        A04
64        A05        A05        A05        A05
65        A06        A06        A06        A06
66        A07        A07        A07        A07
67        A08        A08        A08        A08
68        A09        A09        A09        A09
69        A10        A10        A10        A10
70        A11        A11        A11        A11
71        A12        A12        A12        A12
72        A13        A13        A13        A13
73        A14        A14        A14        A14
74        A15        A15        A15        A15
75        A16        A16        A16        A16
76        A17        A17        A17        A17
77        A18        A18        A18        A18
78        _LPEN        _LPEN        _LPEN        _LP
79        _VSYNC        _VSYNC        _VSYNC        _VSY
80        _CSYNC        _CSYNC        _CSYNC        _CSY
81        _HSYNC        _HSYNC        _HSYNC        _HSY
82                VSS        VSS        VSS
83        DRD15        DRD15        DRD15        DRD15
84        DRD14        DRD14        DRD14        DRD14


8375  SRC: A500 PLUS MAINTENANCE MANUAL
8372  SRC: "FATAGNUS PRESENT DANS LES AMIGA 300" .GIF
8372B SRC: "8372B-AGNUS_PIN.TXT"
8370  SRC: "8370-AGNUS-PLCC.PNG"
[CAUTION: 8372 SRC]
The schematic indicates a oblique pin plcc offset (see included picture)


FatAgnus8372.gif

I am still in need of writting up the 8375 - 318069-02 thats found in the A600, this will complete the primary series of Agnus for the Desktop machines (with the exception of the 8374 - which is called ALICE (thanks rkauer =) ) and found in the A1200/A4000)


So you want 2MB on an an A500 - is it possible?

It sure is, but this comes down to HOW MUCH work you want to do -

Modding the motherboard
In terms of simplist - modifying a motherboard - then you are best to start with an 8372B Agnus and an Rev6a A500 motherboard. From this you will then need to modify the socket to feed of the RAS1 ( pin 58 ) signal to a small PCB that will MUX (multiplex) this signal with the assertion of the upper 1MB of the 2MB structure - its a lot of work, and somthing I certainly plan on doing..... for fun... LOL

Adapter Building
The other method would be to build your own 2MB adapter - from this you can use any 2MB Agnii you wanted - I would recommend an 8375 390544 series or 8372B if you can find one.

once you have ironed out the signals in the right place - you will then need to
1. modify the motherboard to assert Address A20 to use the full 1MB space as CHIP -
2. you will then need to MUX on your adapter board the RAS1 with GARY to address the upper 1MB of 2MB CHIP ram.


So wheres this extra ram go?
Well in either case it could go onto the TRAP DOOR port - this you will use the EXRAM signal line to MUX with RAS1 and the GARY signal to address the upper 1MB - however in the second case it might just be easier to populate the extra 1MB on the Agnus Adapter


hope that helps.
 
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rkauer

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Erm, the equivalent of Agnus on AGA machines is the Alice. Lisa is the succeeder of Denise...

Sorry for the minor correction.
 

Zetr0

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LOL!!!!
whoops

well its what.... 04:01 am here.... I could blame that ;)
 

rkauer

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Also, just in theory you can hook a 2Mb Agnus on a 1Mb Amiga only interfacing with Gary to achieve 1.5/2Mb RAM without a Megachip/MiniMegi.

I'm still scratching my brain out to make the 512kb on trapdoor to work as slow_RAM in one of mine 1Mb-on-board rev.6 A500.

The EX_RAM signal is a funny* thing...:banghead:

*at least the correct word still start with "fu..."
 
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abraXXious

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We are talking about a revision 6.4 A2000, not an A500!

Okiez, so is an 8375b and 8375r2 pin compatible?

---------- Post added at 13:02 ---------- Previous post was at 13:00 ----------

Hey Zetr0,

I know you are busy fellow, but any chance of you looking at the hack (mentioned in one of the first posts) and telling me if it possible to do the hack with an 8375r2 agnus?

Part Number - 318069-10?
 
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