derkom's attempt

[derkom]

H4-011.jpg (182.29 KiB) Viewed 2577 times

H4-012.jpg (83.24 KiB) Viewed 2577 times

Here's a picture so you can see the board and jumpers, but I've triple checked them. Doesn't hurt to have a few more eyes on it though. One thing I haven't checked is to make sure the shunts are actually shorting them, but there's no reason to imagine otherwise. I'll verify that when I pull the board out to look at the soldering again.

Am I remembering incorrectly, or is it not expected to see one bus error during TOS boot, when it determines RAM size?

EDIT: I haven't stock a clock battery in, but that shouldn't matter, should it?

[exxos]

This is the startup..

https://www.exxosforum.co.uk/forum/viewt ... =77&t=1203

I don't know how far it has to go before it sizes RAM.. if that's the case, you should be able to boot from the diagnostic cart.

[derkom]

This is the startup..

https://www.exxosforum.co.uk/forum/viewt ... =77&t=1203

I don't know how far it has to go before it sizes RAM.. if that's the case, you should be able to boot from the diagnostic cart.

Oh right, that's a good point. It's going to check for the diagnostic cart before the expected bus error (and no, I didn't have the diag cart inserted when capturing that data--presumably it would generate the same bus error since it sizes RAM itself).

Since I don't actually know what's on my TOS chip, and I would like one of the "proper" crystals (and our postal strike has mercifully ended), I'll order these from your re-energised shop. At least I can eliminate that unknown factor, if this hasn't all managed to make sense in the meantime. And we can see if the order takes 12 hours to appear.

[exxos]

Since I don't actually know what's on my TOS chip, and I would like one of the "proper" crystals (and our postal strike has mercifully ended), I'll order these from your re-energised shop. At least I can eliminate that unknown factor, if this hasn't all managed to make sense in the meantime. And we can see if the order takes 12 hours to appear.

If the TOS chip is unknown, then you need to read it contents to see what version it is..

OK for order, will keep a closer eye on it know I got a heads up...

[derkom]

If the TOS chip is unknown, then you need to read it contents to see what version it is..

...or if there is anything there at all. I did order a EEPROM programmer so I'd be ready for the upcoming GAL work, and it'll come with an appropriate adapter for this chip as well, but it's lost somewhere between China and here at the moment, so not of much use right now.

OK for order, will keep a closer eye on it know I got a heads up...

Just placed. Naturally I managed to find a couple of other essential items as well. Got the confirmation email myself immediately.

[exxos]

Just placed. Naturally I managed to find a couple of other essential items as well. Got the confirmation email myself immediately.

Got the order.. Very odd goings on.

[derkom]

Using some bodge tape, tape the reset button to keep the machine in reset. Power up the machine and check all the voltages on a 68K expansion socket.

Every pin should have 5V on it. The exceptions are GND,E,CLK,RESET,HALT E & CLK

Okay, I've done this, and when the machine is in reset, I'm getting 0V on D1, D2, D3. All other data and address lines show the anticipated 5V.

This isn't a simple case of "not connected", though, because these data lines are active during a boot attempt:

D0-D4 reset.png (25.3 KiB) Viewed 2537 times

I don't include RESET in that screengrab, but it's low (i.e. button held in) up until the moment where D1-D3 jump high.

Any thoughts on this? Can anyone else observe the behaviour of these lines during reset?

EDIT: And yes, I've confirmed pullups are good all the way across the bus.

[exxos]

As they are switching high and low then should be OK. I can't find in the 68000 manual what state the pins are in during reset.. I just assumed they would go tri-state and go HI.. maybe not then..

[exxos]

Finally found it..

According to this, the databus should go tri-state and float high... Think someone else would have to verify this behavior...

Capture.PNG (104.96 KiB) Viewed 2522 times

[exxos]

Okay, I've done this, and when the machine is in reset, I'm getting 0V on D1, D2, D3. All other data and address lines show the anticipated 5V.

Oh I thought it was the whole databus... Have you double checked you have 2.2K resistance on D1-3 ?