2MB Chip RAM directly on A500 rev. 6 motherboard?

[alexh]

A600 use AGNUS part numbers 390544 only on v1.0 motherboard. They use 318069-10(pal) and 318069-11(ntsc) on motherboards v1.3, 1.5 and 2D. No idea what the pinout differences are (if any).

I found it difficult to read the pin numbers on the A600 schematics I could find online they are too blurry. The ones I found had no validation data either (i.e. you've no idea where they came from, which motherboard version they correspond to or which agnus chip is described on them)

[Metalguy66]

Ok. Heres what is kewl:
According to the service manuals, the A3000 (8372B 318069-03) AGNUS is pin compatable with the rev 6a A500! All of the signals are in the right place. Even the one (pin 41)that controls PAL/NTSC on bootup. According to the information in the Rev 6a a500 schematics, and the A3000 schematics, you should be able to drop an 8372B 318069-03 AGNUS into an A500, add a 74LS139 DEMUX chip to create the 4 separaet CAS signals, add the extra DRAM, and it should work!



SO heres what you do to put 2megs chipram on the motherboard in a rev 6a A500:
First, replace the 8372A agnus with an 8372B 318069-03 AGNUS.
Next, get out your soldering iron and the following materials:
Eight 256k x 4 DRAMs
One 74LS139 demux
Some insulated hookup wire (I use 40ga Kynar)

Add A20 Address line:
1)On the back of the motherboard, Hook a wire from pin 35 of the agnus socket to pin 48 of the 68000 scoket.

Demux original CAS signals with DRA9:
2)bend up pins 7 and 12 of U35.
3)Take the 74LS139 and bend all the pins out horizontal and clip them to about 2mm (1/8" length).
4)hook a wire from pin 8 of U35 to pin 3 of the 74LS139.
5)hook a wire from pin 13 of U35 to pin 13 of the 74LS139.
6)hook a wire from pin 56 of your AGNUS socket to pins 2 and 14 of the 74LS139.

four separate CAS signals:
7)hook a wire from pin 4 of the 74LS139 to the pad on the motherboard where pin 12 of U35 used to be connected.
8)hook a wire from pin 12 of the 74LS139 to the pad on the motherboard where pin 7 of U35 used to be connected.
9)Piggyback 8 more 256k x4 DRAMS on top of the existing 8, bend up pin 17 on all 8 of the added chips. Solder all other pins to the pins on the chips below them.
10.)hook all the pin 17s together on the left 4 (U18,U19,U22, and U23)and also to pin 11 of the 74LS139.
11.)hook all the pin 17s together on the right 4 (U16,U17,U20,and U21) and also to pin 5 of the 74LS139.

clock enable:
12.)hook pins 1 and 15 of the 74LS139 to pin 3 of U33.

Hot, ground, & mounting the extra IC:
13.)hook pin 8 of the 74LS139 to pin 10 of U35.
14.)hook pin 16 of the 74LS139 to pin 20 of U35.
15.)Use hot-glue or double sided tape to secure the 74LS139 on top of some existing IC..

Getting A19, A20, XCLK, and _XCLKEN straight:
16.)Make sure that JP2 and JP5 are set as follows:


DOUBLE CHECK EVERYTHING and make sure nothing is shorted/grounded etc..

NOTES:
Ok.. its possible that DRD9 and CCK might each need about a 10ns additional propogation delay.. I doubt the timing is THAT critical, but I have not built this mod, so I dont know. I will try it as soon as I can get my hands on an A3000 Agnus.

Also, these instructions are assuming that you are starting off with a rev. 6a A500 motherboard that has already been fully populated with 1 meg (eight 256k x 4 DRAMs) of Chipram.

[alexh]

http://aminet.net/docs/hard/2MegAgnus50d5.lha
http://aminet.net/docs/rview/TwoMegAgnus.txt

Heh I guess you couldn't read the A600 one either.

[Metalguy66]

The difference between what I came up with, and what they did is that they are "remaking" a Whole lot of circuits on a custom board, that in fact are already there on the A500 motherboard. I think 11 wires, a $1.00US TTL IC, and 8 DRAM chips is a WHOLE LOT easier than either of those "projects".. Also, if I was going to go to the trouble of designing a board with a custom PAL, I'd DAMN SURE use higher density ram. 1 or 2 chips at the most.

What I outlined above is the simplest way to do it, and its exactly the way the A500+ does it (minus some dampning resistor packs which you dont need if you are piggybacking the chips and thus sharing common adress & data bus paths)

Yeah I can read my A600 schematics.. As I said. Theres about 20 pins "difference" between the A500+/A600 AGNUS(es) and the A500 8372A 1meg AGNUS.

Both the schematics I used to come up with the upgrade instructions (A3000 and rev6a A500) Actually have the relevant AGNUS part number listed in the schematic.

I would also add that upgrading via my instructions will not "get in the way" of an internal accelerator. Any of those "plug in" agnus boards negate the prospect of using an internal accelerator and putting the stock A500 case back together. Theres just not enough clearance under an accelerator to fit a "Megachip" style agnus-socket board. And if you space the accelerator up at the 68000 socket, you'll never get the keyboard/top case half to go back on the machine. Internal A500 Accelerators BARELY fit "as-is"...

Also, if you use one of the "non-a3000" versions of the 2-meg AGNUS, you are going to be locked in either PAL or NTSC (at least for boot-up purposes) whereas the A3000 agnus actually has the PAL/NTSC mode switch pin in the right place to work with the rev 6a A500's JP4 jumper.

If someone will donate (or sell cheap) an A3000 8372B 318064-03 AGNUS chip, I will do this mod on my own rev 6a A500 motherboard to verify that it works and all the DRAM timing characteristics are right.

[czarek]

WOOOW - you're the man! Thanks a lot - though that sounds pretty hardcore, especially demuxer chip and all lines to connect it. So one more stupid question (Sorry). If I replace my Agnus with 8372B, add A20 address line, will it allow me to use memory from expansion slot or is it basically the same thing?

[amigaksi]

>by alexh on 2008/10/18 5:25:55
...
>8375 318069-11 replace it with 8375 318069-10
>8375 390544-02 replace it with 8375 390544-01
>8375 318069-19 replace it with 8375 318069-18

...

>It's an A500+ (rev 8a)

I just opened up the A500 and it does state A500+ on the motherboard and is rev. 8A.  It has 390544-01 8375 and boots as PAL by default unless I go to the startup-menu.  Anyway to make it boot as NTSC by default without cutting traces or soldering? Some applications/games don't seem to care what the startup-menu boots up as.

[Metalguy66]

czarek wrote:
WOOOW - you're the man! Thanks a lot - though that sounds pretty hardcore, especially demuxer chip and all lines to connect it. So one more stupid question (Sorry). If I replace my Agnus with 8372B, add A20 address line, will it allow me to use memory from expansion slot or is it basically the same thing?

It's not "hard core"... Its dirt-simple...

No, just adding the A20 adress line won't do anything. You have to DEMUX CAS/DRA9 in order for the agnus to adress 2 megs of chip ram. It doesnt matter whether the memory is on the motherboard, or in the trap door slot.

 If you have a rev 6a A500 with 1 meg of chipram already on the motherboard and you want to use memory in the trap door slot for an extra meg of chip ram, follow the same instructions as I posted before, EXCEPT you hook the wires that go from pins 5 and 11 of the 74ls139 to pins 35 and 36 of the trapdoor slot connector (INSTEAD of hooking them to the two groups of pin 17s on the piggybacked ram chips). Also, you must first cut the motherboard traces that go to pins 35 and 36 of the trapdoor connector. Once this is done, you should be able to plug in an A501+ (or other 3rd party) 1 meg expansion at the trap door slot and have it adressed as the second meg of chip ram.  

[Metalguy66]

I just opened up the A500 and it does state A500+ on the motherboard and is rev. 8A.  It has 390544-01 8375 and boots as PAL by default unless I go to the startup-menu.  Anyway to make it boot as NTSC by default without cutting traces or soldering? Some applications/games don't seem to care what the startup-menu boots up as.

Yes its very easy to put 2 megs chipram on an A500+ (rev 8a) motherboard.

The A500+ (8a) motherboard already has the 74LS139. Its marked as U32 on the motherboard. To put 2 megs chipram on the motherboard, just piggyback another 8 chips, bend up all the pin 17s, and hook the left 4 pin 17s to pin 11 of U32, and the right 4 pin 17s to pin 5 of U32. It's that simple.

As far as hard-switching PAL/NTSC, I dont believe that the 8375 agnus has that capability. On the 8372 version, grounding pin 41 of the agnus makes it default to NTSC. Leaving it open (or hi) makes it default to PAL. I dont believe this pin is in the same place on the 8375, if it even has it. The 8375s are listed as either PAL or NTSC specific chips.

[amigaksi]

>Yes its very easy to put 2 megs chipram on an A500+ (rev 8a) motherboard.

>The A500+ (8a) motherboard already has the 74LS139. Its marked as U32 on the motherboard. To put 2 megs chipram on the motherboard, just piggyback another 8 chips, bend up all the pin 17s, and hook the left 4 pin 17s to pin 11 of U32, and the right 4 pin 17s to pin 5 of U32. It's that simple.

My a500+ slot has the additional meg without any jumpers/piggybacking so I guess all the signals that are needed must be there in the slot connector.  However, I do have an Atari 520ST that uses a similar method you mentioned to expand it's memory.

>As far as hard-switching PAL/NTSC, I dont believe that the 8375 agnus has that capability. On the 8372 version, grounding pin 41 of the agnus makes it default to NTSC. Leaving it open (or hi) makes it default to PAL. I dont believe this pin is in the same place on the 8375, if it even has it. The 8375s are listed as either PAL or NTSC specific chips.

Is that pin 41 on 8372 an input to Agnus?  If so, which chip is it coming from-- perhaps easier to ground the signal from the source since Agnus is a square chip and it's very hard to ground a pin w/o cutting trace or soldering.

[Metalguy66]

My a500+ slot has the additional meg without any jumpers/piggybacking so I guess all the signals that are needed must be there in the slot connector.

Ok. The trap door slot is NOT the motherboard.. Yes, it's common knowledge that you can have the additional meg of chipram in the Trap door slot. That is what the A501+ is for (theres also many aftermarket versions of the 1 meg chipram trap-door expansion card for the A500+). In this thread, we have been talking about putting all 2 megs ON THE ACTUAL MOTHERBOARD of both rev 6a A500 and rev 8a A500+ machines.

However, I do have an Atari 520ST that uses a similar method you mentioned to expand it's memory.

I'm sorry.  Yeah I have an ATARI ST too. It makes a good wedge-shaped doorstop to hold the bathroom door open and let the place air out after someone has taken a huge dump.

Is that pin 41 on 8372 an input to Agnus? If so, which chip is it coming from-- perhaps easier to ground the signal from the source since Agnus is a square chip and it's very hard to ground a pin w/o cutting trace or soldering.

Yes, the PAL/NTSC jumper(JP4) is an input to agnus on the rev 6a A500 board. It goes to pin 41 of the 8372(a or b) AGNUS. If you close the jumper, it grounds the pin, and tells AGNUS to boot in NTSC mode. If the Jumper is left open, the input floats "hi" and AGNUS boots in PAL mode. Some A2000 motherboards have a similar jumper. It has been common practice to hook a switch to this jumper. On earlier rev. 5 A500 motherboards, there is no jumper, so you have to hook the switch in between pin 41 of the AGNUS socket and ground.

YOU CAN'T DO IT WITH AN 8375 AGNUS...  And you can not put an 8372(a or b) in an A500+ agnus socket because they are not pin-compatable. Theres about 20 pins that are "rearranged" between the two.

So basically, be happy with your PAL machine..

 

[czarek]

Hey I just found those two schematics:
http://falba.net/upload/a500.gif
http://falba.net/upload/a500plus.gif
They look very similar, so maybe there would be the way to make some rewiring between motherboard and Agnus socket or make some adapter so I could use 8375 Agnus? I already have couple of them so it would be no problem with getting one, and 8372B is pretty rare as it was only used in A3000s...
Or is it too much hassle?

[alexh]

The schematics look similar but the pin numbering is subtly different. Enough to make re-wiring a no go.

[Metalguy66]

How about OVER 20 PINS ARE DIFFERENT between the rev 6a a500 and rev 8a a500+ agnus sockets.

Go back and reread this thread... And think about it REAL HARD.. The two agnus pinouts I posted were from the REV 6a A500 and A3000 schematics. They are VERY CLOSE.. Only 3-4 pins difference. And the A3000 agnus gives you switchable PAL and NTSC. The 8375 DOES NOT.. It's "hard wired" as either PAL or NTSC.


For a rev. 6a A500, you have 3 options:

a) Buy a plug-in 2-meg AGNUS board such as the DKB megachip.
b) Follow the instructions that I outlined and use an A3000 agnus.. (its damn simple.. ALOT simpler than trying to relocate 20+ pins on a PLCC chip.)
c) Buy a rev 8a (a500+) Motherboard which is already wired correctly for the 8375 agnus.

As far as the 8372B 318069-03 AGNUS being "rare"?
Well, A3000s are turning up dead from clock battery leakage all the time. If you ask around, you can probably find someone who will sell you the AGNUS out of a "dead" machine.

Here is a website that claims to have 5 in stock:

http://www.oldsoftware.com/CBMchips.html

[amigaksi]

>Yes, the PAL/NTSC jumper(JP4) is an input to agnus on the rev 6a A500 board. It goes to pin 41 of the 8372(a or b) AGNUS. If you close the jumper, it grounds the pin, and tells AGNUS to boot in NTSC mode. If the Jumper is left open, the input floats "hi" and AGNUS boots in PAL mode.

Okay, my other A500 w/1MB chipram (rev. 5A) does not have a jumper for NTSC/PAL so I think breaking pin 41 would have the same effect.  I don't need the PAL functionality.  I was asking whether there was a better spot where that disconnect can be done.

>YOU CAN'T DO IT WITH AN 8375 AGNUS... And you can not put an 8372(a or b) in an A500+ agnus socket because they are not pin-compatable. Theres about 20 pins that are "rearranged" between the two.

>So basically, be happy with your PAL machine..

How about putting a PAL->NTSC decoder on the output.  I see some on Ebay.

[Metalguy66]

Yeah. Unfortunately, on a rev. 5 NTSC A500, pin 41 of AGNUS is permanently grounded, and the trace that goes from pin 41 to ground is on the top side of the board, covered by the agnus socket! This sucks... So to install a PAL/NTSC switch on a rev 5, you have to bend up the pin on your actual agnus chip, and solder a wire to it, then hook a switch that toggles it to ground.

Im not going to go into the specifics of Scan-converters in this thread. Just be careful what you buy, and know that this is not going to change anything about software compatability.

Also, I dont have any problem running NTSC software in PAL mode on my PAL A500+. The NTSC software's display just doesn't take up the full screen. What I run into MUCH more often is older Games/Demos that require Kickstart 1.3.. A kickstart switcher fixes this problem. The other compatability problem that I run into quite often on older demos is coding that INSISTS on the presence of 16-bit FASTRAM (mapped at C00000.) This is a problem because my system does not have any 16-bit Fastram. Only 32-bit fastram.

Both of these issues are examples of Coders who did not follow the guidelines in the Hardware Reference Manual and/or Rom Kernal Reference Manual. Any "well written" software from the KS 1.3 era should work fine with KS 3.1 if the coders paid attention to Commodore's reccomendations.. Unfortunately, this is not alwayse the case.

There are Software based "degrader" utilities available that attempt to fix both these issues, but they do not work in all cases.


 

[Metalguy66]

Ok. Im bumping this thread back up, because I like talking about A500 stuff...

Converting a rev 6c A501 into an A501+

So you got a rev 8a A500+ motherboard.. Its got a nice 8375 2meg AGNUS chip, but only 1 meg of chipram on the motherboard. If you want 2 megs of chipram, you generally have 2 options.

1)piggynack 8 more 256k x 4 DRAMs on top of the existing ones on the motherboard.

2)Buy an A501+ (or aftermarket equivelant) that puts an extra meg of chip ram in the trap door expansion slot.

Both of these are fine alternatives.. But if you have an old A501 (512k expansion) laying around that you arent using, you can easily upgrade it to a full meg, providing a third alternative for gaining 2 megs of chipram.
Heres how:

NOTE: This will only work on the rev 6c A501 board. If your A501 is one of the earlier revisions that has 16 DRAM chips, this mod will not work!

1) Find jumers JP2 and JP3 on the A501 card. These are set to enable the "refresh kludge" from the factory. We dont need a "refresh kludge" because our our 8375 generates refresh signals to handle the full 8-bits of row adressing needed by our 256k x 4 DRAMs. So get a razor blade or X-acto knife, and carefully cut the tiny trace that goes between the center and upper pad of JP3. Then cut the tiny trace that goes between the center and lower pad of JP2. Now put a blob of solder to connect the center and lower pad of JP3. Add a second blob of solder to connect the center and upper pad of JP2. CHECK YOUR WORK WITH AN OHM METER!

2) Now get 4 extra DRAM chips. These should be 20 pin DIP package, 256k x 4, 120ns or faster. Bend up pin 4 on each of these DRAMs.

3) Piggyback each DRAM on top of one of the 4 DRAMs on the A501 board. Solder all pins to the chip below, except pin 4 (which should be bent up.)

4) Solder a wire connecting all of the bent up pin 4s, and also connecting to the solder pad directly above JP9. (see picture)
This creates the additional RAS signal we need for the extra 4 DRAMs.


Thats it! Stick it in your A500+, boot it up, and you should have 2 megs of Chip Ram.

What about the Realtime Clock you ask?

By default, your Rev 8a A500+ motherboard will use it's on-board RealTime Clock, and ignore the one on the A501 card. If you would like it to use the Realtime Clock on the A501 card, then close jumper JP9 on the A500+ motherboard.