TF536/68000 switching

[derkom]

I'm surprised I haven't found this discussed before, and forgive me if I just missed it in the search...

Is it feasible to build a system with the TF536 that is 68030/68000 switchable, like the CT60e can switch 68060/68030 on the Falcon? I don't have a built up TF536 yet, but I tried sticking two 68000 chips in my H4, with the VCC pins disconnected on one of them, and sadly that does not work, and the system won't boot.

I'm hoping eventually to shoehorn a TF536 into my Stacy (don't know if this can be made to fit, but I'm giving it a go), and since the Stacy isn't something that can easily be opened up, it would be nice if there were some way to switch back to the 68000 for compatibility without having to remove the TF536.

[terriblefire]

I'd asked this already somewhere.. Its not possible to disable the H4 onboard 68000. Its something i'd like to see in the H5.

[derkom]

I'd asked this already somewhere.. Its not possible to disable the H4 onboard 68000. Its something i'd like to see in the H5.

Well the H4 was really just for testing out if I could stick two 68000 chips on the bus, and disable one of them simply by removing VCC from it. I figured if that worked, I could try wiring up a switch to provide power either to the 68000 or to the TF536 in the Stacy. Since that does not work with two 68000 chips in the H4, I am guessing it also won't work with one 68000 and one TF536, although I'll certainly test this later.

Obviously if one could successfully switch all 64 pins, that would certainly work, but that's clearly not feasible. So the question is: Is there any feasible way to do it?

[terriblefire]

Obviously if one could successfully switch all 64 pins, that would certainly work, but that's clearly not feasible. So the question is: Is there any feasible way to do it?

I dont think there is a way to stop the onboard 68000s running on ST type hardware without taking out the entire DMA system. I could be wrong but just based on the knowledge i currently have loaded in my RAM the only way to stop the onboard 68000 is to assert BGACK ... which i think would stop everything else working... like floppy drives. Someone will correct me if im wrong.

[derkom]

I dont think there is a way to stop the onboard 68000s running on ST type hardware without taking out the entire DMA system. I could be wrong but just based on the knowledge i currently have loaded in my RAM the only way to stop the onboard 68000 is to assert BGACK ... which i think would stop everything else working... like floppy drives. Someone will correct me if im wrong.

I'm talking a far more basic approach here, of electrically "switching off" the 68000. In my test on the H4, I put DIP 68000s in two of the expansion sockets (having removed the PLCC 68k, and verifying it will boot off either DIP alone), and then literally just bending out both of the VCC pins on one of them, so that it should just be a dead chip at that point, no power. But unfortunately even without power, it seems to be soiling the bus in some way.

[exxos]

Disabling the 030 is likely easier then the 68000 as the 030 has a PLD linked to it. Holding the 030 in reset and disabling e-clock etc in firmware. The 68000 still generates e-clock and would need logic to disable it.

There may well be other signals which would need isolating as well. Basically you have 2 CPUs on the same bus and they both can't signals at the same time. Might be others which need isolating also. Its jut not high up on my to do list.

But there are other problems currently to solve yet as addons like flashy clock assume the 68000 is used. A booster in a expansion port won't play nice with flashy yet. But I need to finish flashy clock first then work on other issues.

Its the same problem I had on the H4 that I was trying to design the flashyclock port when i hadn't designed flashyclock itself yet. Its very difficult to do. Things need doing in a proper order and there's lots to do yet.

My store is soaking up my time and if people want the H5 anytime soon, then all these issues will have to wait. Otherwise I will need to finish all the addons then work on motherboard fixes which will probably drag on for the next couple of years.

So yes it could well be done. But other work needs doing first and solving and there's only 1 already burnt out exxos who doesn't have much time for development work these days

[exxos]

@derkom removing power isn't a good idea. Likely you will damage stuff doing that.

Holding the CPU in reset will tristate a lot of pins, but not all, and those have to be isolated with external logic. Same goes for a 030 card, it will need extra logic to turn it off. So it would likely ended up with a PLD to control all the switching .

[czietz]

The venerable PAK/2 accelerator (1990 vintage) already had the capability to switch between accelerated CPU (68020) and 68000. For that, it had to switch three CPU signals: BR, BG, and E. This article is in German but Google Translate and the GAL equations should give you the required information: http://www.skulimma.de/PAK68_2.html

[derkom]

The venerable PAK/2 accelerator (1990 vintage) already had the capability to switch between accelerated CPU (68020) and 68000. For that, it had to switch three CPU signals: BR, BG, and E. This article is in German but Google Translate and the GAL equations should give you the required information: http://www.skulimma.de/PAK68_2.html

Ah, that may be very helpful. Thank you! I was already planning to try pulling up some of the other, non-address and non-data pins, to see whether some combination worked, but this will save me some effort.

[exxos]

@czietz doesn't that assume the 68000 is plugged ontop of the pak ? Things could get more of a problem when the CPU is on the motherboard.

But if people want to look into it, then that's fine. Just be warned that you may have to undo such changes if using future H4/5 addons.