Project STacy (STaceX, TOS 2.06 & others)

General discussions or ideas about hardware.
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rpineau
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Re: Mega Bus -> 68K Adapter

Post by rpineau » Mon Sep 18, 2017 6:45 pm

The signals go from the Mega bus to the 74L248 (INTx) to the CPU IPLx lines

MegaBus ===> 74LS148 ===> CPU IPLx
and yes they get used. they are interrupt lines so that cards on the Mega Bus can trigger interrupts at level 3, 5 and 7 (NMI).
As for the monster .. no idea as I don't have one an never looked at it.
Working ones : MegaSTE (68020) / TT030 / Falcon with AB040 & Eclipse / 1040STF
Need testing : Falcon with CT2

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Re: Mega Bus -> 68K Adapter

Post by Atarian Computing » Mon Sep 18, 2017 6:53 pm

Thanks again. What I'm trying to achieve is full pin compatibility for Mega Bus with 68K CPU in order to use accelerators and such on the Mega Bus.

For example: PAK -> 68K Adapter -> Mega Bus

Would I have to add IPL lines to the 68K adapter from the main board in this case?

Note that this is not for a Mega ST but a project I'm planning where space is an issue.

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Re: Mega Bus -> 68K Adapter

Post by rpineau » Mon Sep 18, 2017 7:37 pm

So you're trying to modify the mega bus to make it a 68K bus ?
Working ones : MegaSTE (68020) / TT030 / Falcon with AB040 & Eclipse / 1040STF
Need testing : Falcon with CT2

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Re: Mega Bus -> 68K Adapter

Post by Atarian Computing » Mon Sep 18, 2017 7:40 pm

rpineau wrote:
Mon Sep 18, 2017 7:37 pm
So you're trying to modify the mega bus to make it a 68K bus ?
Essentially, yes. Is it even possible?

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Re: Mega Bus -> 68K Adapter

Post by rpineau » Mon Sep 18, 2017 8:57 pm

why not just take a 64 pin DIN connector and wire it from the 68K. Just use the same pinout as the Mega bus and only replace what's not present (like INT pin are replaced by IPL pins) as you don't intend to connect any Mega Bus card on there (?) .
If you explain the final intent we probably can give you better answer.
Rodolphe
Working ones : MegaSTE (68020) / TT030 / Falcon with AB040 & Eclipse / 1040STF
Need testing : Falcon with CT2

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Re: Mega Bus -> 68K Adapter

Post by Atarian Computing » Tue Sep 19, 2017 4:51 am

rpineau wrote:
Mon Sep 18, 2017 8:57 pm
why not just take a 64 pin DIN connector and wire it from the 68K. Just use the same pinout as the Mega bus and only replace what's not present (like INT pin are replaced by IPL pins) as you don't intend to connect any Mega Bus card on there (?) .
If you explain the final intent we probably can give you better answer.
Rodolphe
Yeah, I might as well reveal my plans. This would be for the STacy. It has a spot for a 100% compatible Mega Bus connector. I want to populate it with an adapter that fits on the motherboard. It will have 2 Floppy cable connectors for cables that extend the bus. From there you can attach either a Mega Bus connector for existing expansions such as a Magnum ST or a 68K adapter for accelerators or MonSTEr.

I don't want to hack anything on the STacy board. Also the 68K is under the DC to DC board so space is an issue. Sure, Darklord has installed a PAK directly on the board but I want to avoid that.

How critical is timing in my case? Would I have to make sure all traces are of equal length on the adapter that plugs on the STacy?

Thanks.

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Re: Mega Bus -> 68K Adapter

Post by IngoQ » Tue Sep 19, 2017 8:46 am

I have to admit, I am not that much of an expert regarding hardware. But if you would want to use the MegaBus as a CPU connector for a CPU replacement, wouldn't you need a way to disable/disconnect the CPU?
Ingo :geek:

| Atari 1040STE@32MHz | Amiga 1200 (ACA1220) | Atari 800XL (U1MB, SIDE2) | Atari 130XL (Sophia DVI) | C64 (1541 Ultimate II, Rev3 RFMod Replacement) | TI 99/4A (F18A, 32k, FlashROM 99) | Sinclair ZX Spectrum 128 (Stereo, DivMMC) | Amstrad CPC664 (512k, M4 Wifi) | ... |

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Re: Mega Bus -> 68K Adapter

Post by Atarian Computing » Tue Sep 19, 2017 9:04 am

IngoQ wrote:
Tue Sep 19, 2017 8:46 am
I have to admit, I am not that much of an expert regarding hardware. But if you would want to use the MegaBus as a CPU connector for a CPU replacement, wouldn't you need a way to disable/disconnect the CPU?
I believe so. I also understand it to be a trivial thing to do. Less invasive than removing it. You could also put a switch on it?

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Re: Mega Bus -> 68K Adapter

Post by IngoQ » Tue Sep 19, 2017 9:08 am

If your goal is to have the 68k bus available, and have the CPU (optionally) disabled (or better: disconnected), I would remove the CPU and replace it with an adapter board. On this you place the CPU in a socket (maybe use the PLCC version to save space), and have the CPU lines fan out on a separate connector.
Ingo :geek:

| Atari 1040STE@32MHz | Amiga 1200 (ACA1220) | Atari 800XL (U1MB, SIDE2) | Atari 130XL (Sophia DVI) | C64 (1541 Ultimate II, Rev3 RFMod Replacement) | TI 99/4A (F18A, 32k, FlashROM 99) | Sinclair ZX Spectrum 128 (Stereo, DivMMC) | Amstrad CPC664 (512k, M4 Wifi) | ... |

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Re: Mega Bus -> 68K Adapter

Post by Atarian Computing » Tue Sep 19, 2017 9:34 am

Well, the more I think of it, the more I suspect a 68K bus through STacy Bus is not a good idea. There would no doubt be timing issues and other problems with accelerators. I will keep this 100% Mega Bus compatible.

I was not planning to make any announcements at this point but since my intentions have been revealed, I might as well make it official. I ask the mods to merge (if possible) this thread with my "Project STacy" thread: viewtopic.php?f=29&t=159

This adapter will be called STaceX

STace is short for Stacy and is commonly used in it's place (rhymes with place). X is for eXtension or eXpansion. Pronounced the same as SpaceX, which is where I got the inspiration for the name.

The whole idea is to utilize the unused and unpopulated expansion slot, which is 100% compatible with Mega Bus. There are no 41612 connectors available anywhere. That is the same as a VME connector but with 24pins in 3 rows. This is why I have to make an adapter with 3 header strips and route the signals to two 34-pin floppy connectors that carry the signals to the Mega Bus via ribbon cables. End result should be that any Mega ST expansion card should work.

My idea was to provide 3 PCBs. The STaceX itself and two cards. One with the Mega Bus connector and one with the DIP64 socket. The point of the DIP64 socket was to eliminate a redundant Mega Bus adapter to be able to use AlanH's MonSTEr card. You would have STaceX -> Mega Bus -> Alan's DIP64 adapter -> MonSTEr. By providing a DIP64 socket that connects directly to the STaceX we would eliminate one step and save space.

This is why I asked about the IPL signals originally. Since Alan's DIP64 adapter is made for the Mega ST's Mega Bus and there seems to be no circuitry from what I can see from his pictures, I have to assume that theyare not connected at all, or connected somehow to the INT and NMI signals on the Mega Bus.

So this is the master plan. Main idea is to use cards such as Magnum ST, MonSTEr, GFX cards etc.

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