I already see your problem ...

Use a cable like this:

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The order of the threads is changeable.

I have added an upper picture of the second version of Saint's expansion here.

BTW, you mentioned earlier that you were going to contact SainT and see if he would share the schematic/Gerbers for his expansion board. Did you ever get a response from him?
I see that he's been on the AtariAge forum recently, so he's still around.

Someone who speaks good English can ask here...

I have already asked him by mail. I am waiting an answer.

It's OK then...  We hope he will respond

Wow - great work! Not worrying about the order of the address and data lines makes life much easier doesn't it?

I'm afraid I'm not good enough at electronics to reliably check it. Although I do have a question for my own learning if that's okay. Why are there 3 capacitors? When I designed my [amateur] expansion I just had one capacitor to smooth the supply to the 512k chip. So it turns out I should have put one on the ATF16V8 as well. But why the 3rd capacitor?

Basically I didn't really know what I was doing and was amazed that what I did worked at all.

Thanks for the info. Starts to make sense now.

Good luck with adding the Flash ROM. I expect you know already but the original EXOS will only find ROMs in segments which are multiples of 16. So you'll need Zozosoft's unofficial EXOS upgrade to recognise system ROMs that don't start on 256k boundaries. 

Once they will add the Ram expansion, adding Zozo's modified EXOS seems a trivial step.

I agree ... if you've already had to get inside the Enterprise to solder wires onto the EXP2 connector, then adding one more wire so that you can use EXOS 2.4 seems pretty trivial.

Great decision to put a FlashRom. Adding the /WE signal even can allow to write it in situ. Don't use Winbond or other cheap makers, better AMD. Zozo can modify his SD cartridge flasher for your memory expansion.

A good range to put a 512KB Rom zone is 60-7F, said by Zozo that it is a scarcely used  area. And for the Ram, like Saint's expansion, filling F0-FB, E0-EF, DC-DF, if 512KB, or F0-FB, E0-EF, D0-DF, C0-CF, BC-BF if 1MB.

Simbiface3 also uses 60-7F as a Rom zone but it can put the Roms in any place so no problem.

From what I can see, AMD don't *seem* to be making 5V flash chips anymore, especially in PDIP format.

The modern 5V part that is being recommended to me is Microchip's SST39F040, which uses the same pin layout as AMD's old 29F040.


Unless I change the address decoding logic from the simple 74HCT138, then I can't decode any of those ranges like that.

The obvious choice would be to use output 4 on the 74HCT138, which would decode to banks 80h-83h, 88h-8Bh, 90h-93h, 98h-9Bh, A0h-A3h, A8-ABh, B0h-B3h, and B8-BBh.

The other choice would be to use output 2 on the 74HCT138, which would decode to banks 40h-43h, 48h-4Bh, 50h-53h, 58h-5Bh, 60h-63h, 68-6Bh, 70h-773h, and 78-7Bh.


Is there a list anywhere of what expansion-bus cards use which segments?

Great decision to put a FlashRom.

I've been looking at this all day, and I'm afraid that I can't find any way to add that PDIP socket for the FLASH chip, and still end up with any kind of sensible board layout.

I'm sorry, I just don't have good enough design skills, and so I'm going to have to abandon the FLASH idea, and just keep the board as a simple 512KB SRAM expansion.


People who need lots of FLASH ROM space already have the Symbiface3 card that you've done such excellent work on, and perhaps in the future they'll also have Pear's lovely looking Dream Turbo Card.

Unfortunately i did not find any documentation, but i am nearly sure that at 80 and above it there is no ROM defined, between 40-7F the chance is a bit bigger, but there should not be so much.

This is the only thing that I could find.

Looking at that, there doesn't seem to be any conflict with the 74HCT138 segment mappping for the SRAM that I am proposing to use, even if it is a bit wasteful.