TF536/68000 switching

[derkom]

Okay, I confirm that with BR, BG, and E disconnected on one 68000, the H4 will run the diag software with both chips on the bus. Whether or not this can translate into a switchable TF536 is another question, and one I can't test until I have a working 536, but at least this is something to go on. Thank you, @czietz!

[czietz]

@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.

In case of the PAK, the 68000 is in indeed on top. But the three signals I mentioned are the only ones that are not connected straight through. Thus, (without thinking it through in detail) it should also work with the CPU on the motherboard, if you break the three signals.

[PhilC]

Breaking the signals on the TF536 could be as simple as not soldering those pins on the DIL cpu header and routing them through a switch, pld etc.

[derkom]

Breaking the signals on the TF536 could be as simple as not soldering those pins on the DIL cpu header and routing them through a switch, pld etc.

Oh sure, I'm already having to build a custom relocator board to make the TF536 hopefully fit in the Stacy, so incorporating the necessary signal breakages/reroutings is easy enough. I just don't know if the TF536 will actually sit quietly on the bus without them like the 68000 does. Only way to find out is to test, which I'll do once I have the built 536.

I already sent off a design for a first attempt at the relocator, naively hoping that breaking VCC would do what I need, but I did at least make it solder blob reconnectable in the design. I can at least test for fit with that board, and if I find that switching those three does work with the 536, and that it fits, I'll make a second version incorporating whatever I need there.

[PhilC]

@derkom your TF536 is at least in the right country now

[derkom]

@derkom your TF536 is at least in the right country now

Barring polar bear attack, it'll arrive next week.

[PhilC]

Barring polar bear attack, it'll arrive next week.

And to think our posties complain about dogs, can't imagine how they'd get on with polar bears

[terriblefire]

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.

Don't ever leave a chip on a bus with no power on... the results are unpredictable.. the 68000 could still get enough power to run via the protection diodes .. or at least enough power to go nuts and crash things. If you're gonna do this you need to modify your machine to be able to isolate the arb lines and E.

[derkom]

If you're gonna do this you need to modify your machine to be able to isolate the arb lines and E.

So it seems. So, since the answer isn't powering things down, this raises another question: If I'm isolating the TF536 this way, will the altram and IDE interfaces still work? I'll have IDE on the Lightning anyway, and was expecting to use that since it would always be present, whether running 68000 or 68030, but now I'm wondering if the TF536's IDE might also be present all the time, even if the 68030 isn't answering. Obviously I can figure this out by testing, but perhaps you already know the answer.

[terriblefire]

So it seems. So, since the answer isn't powering things down, this raises another question: If I'm isolating the TF536 this way, will the altram and IDE interfaces still work? I'll have IDE on the Lightning anyway, and was expecting to use that since it would always be present, whether running 68000 or 68030, but now I'm wondering if the TF536's IDE might also be present all the time, even if the 68030 isn't answering. Obviously I can figure this out by testing, but perhaps you already know the answer.

No the altram and IDE only respond to the 030 lines.