Mega ST project

[HigashiJun]

Quick edit:

MC68HC000 CPU also runs fine (PAK mode and fallback mode).

Something was probably connected wrong yesterday...

[HigashiJun]

The relocator pcb and the pak can be the problem. I have a extension for the mega st bus connector to test it ...


mst_extension.jpg

Hello Frank,

I have tried your VOFA adapter (so no CPU relocator, as the PAK and VOFA can fit without any problem) with my PAK68 and the result is the same. I have a freeze when the VGA driver starts to load (Idek driver and NVDI 5.03).

I have also tried the STGA30 driver, but I have a freeze.

So the CPU relocator is not the problem here.

[frank.lukas]

What pullups have you on the board?

[HigashiJun]

What pullups have you on the board?

If you mean the bus resistors on the motherboard, they are as per Exxos' recommendation, i.e. address bus and data bus are 2.2k Ohm.

[HigashiJun]

Ok , I have sorted all issues out.

The FDD now works fine. I was fiddling with PAK68 jumpers settings and I realized jumper J9 was set to synchronous clock...

Once set to asynchronous, everything started to work as expected, but not at 50 Mhz... :(

The Mega ST starts to boot at 50 Mhz but then freezes with 4 bombs after an error free memory check.

So I have (for the moment ?) to go with 32 Mhz.

I will buy a 40 Mhz oscillator and check if I have more success than with 50 Mhz.

What is strange is that CENTBENCH sometimes shows the right CPU speed, i.e. 32 Mhz and sometimes dispalys a wrong value, like 19 Mhz...

The FPU speed is always accurate.

[HigashiJun]

EDIT: I managed to run the Mega ST at 50 Mhz, but without the HDD.

Booted normally, but I had corrupted TOS menus.

[HigashiJun]

I finally have a better view of what would my Mega ST look like when this project is finished.

MegaST.jpeg

There are still some issues to overcome, but if everything comes together, it should be the final version.

I am still hesitating concerning the CD-ROM drive, but hey, we are in 2022 soon and the already existing USB solution is very useful...

As the CPU relocator works reliably with the 68HC000 only, I am waiting for a 4 layer PCB relocator. It is actually in production at JLCPCB and should be delivered soon.

The current IDE ribbon might be replaced by the following IDE-CF adapter:

IDECF.jpg

The other things to do are:

- Think where to fit the USB ports
- Think where to fit the Tweety Board connector (I already have an idea)
- Think whether to add a 68000/68030 switch for the PAK68 fallback mode
- Find a place to fit the LED from the Lightning ST

And that should be all...

[rubber_jonnie]

Wow, that's jam packed!! Nice one.

[HigashiJun]

Wow, that's jam packed!! Nice one.

Thank you !

Yeah, a sandwich in a pizza box.

:D

[Darklord]

Congratulations on getting your "mega" project to this point. :)

I put the USB ports in the expansion cover on the back of the
Mega ST for my Lightning ST setup. Dead handy.

I suppose it would be much more convenient and accessible
if one could have them in the front casing but I was afraid
that I would mar the looks of my machine...

Mega ST4-Lighnting ST01.JPG