Mega ST project

General discussions or ideas about hardware.
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HigashiJun
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Re: Mega ST project

Post by HigashiJun » Wed Oct 13, 2021 10:32 pm

Thank you for all your suggestions.

All mandatory fixes are done as per Exxos' recommendations (except 1771 pull-ups as I have an original FDD).

I will try Frank Lukas' trick to see if it helps.

Cheers.

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HigashiJun
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Re: Mega ST project

Post by HigashiJun » Mon Oct 18, 2021 11:01 am

Before trying Frank Lukas' suggested trick, I wanted to check how my setup and the CPU relocator will cope with a low-consumption MC68HC000.

So I have ordered a MC68HC000 on EvilBay and it has just arrived today.

MC68HC.jpeg
MC68HC.jpeg (351.46 KiB) Viewed 266 times

I have fitted it in the relocator and then fitted the relocator itself in my Mega ST.

And the result is: no more RAM errors, freezes nor reboots, even with the blitter on.

So far, so good...

Let's try with the Lightning ST fitted (and fingers crossed):

LIGHTNING.jpeg
LIGHTNING.jpeg (439.92 KiB) Viewed 266 times
FINAL.jpeg
FINAL.jpeg (365.39 KiB) Viewed 266 times

SUCCESS ! :D

No errors, RAM issues, freezes or reboots any more.

Next step is fitting the STGA and checking the result.

STGA.jpeg
STGA.jpeg (417.04 KiB) Viewed 266 times
OK.jpeg
OK.jpeg (358.06 KiB) Viewed 266 times

And success again ! :D :D :D

Everything works as expected and is rock solid !

These MC68HC000 seem to be a real cure to STs and STEs having some weird issues, and I could only recommend them to all.

OK, now will come the hardest part: trying to make the PAK68/3 work with all this stuff, but it is not for now.

Cheers.

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exxos
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Re: Mega ST project

Post by exxos » Mon Oct 18, 2021 11:25 am

That is really strange. HC will only generally work when bus resistors are changed and in general make problems worse on machines otherwise.

Could your original CPU be faulty ?
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HigashiJun
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Re: Mega ST project

Post by HigashiJun » Mon Oct 18, 2021 11:35 am

exxos wrote:
Mon Oct 18, 2021 11:25 am
That is really strange. HC will only generally work when bus resistors are changed and in general make problems worse on machines otherwise.

Could your original CPU be faulty ?
As stated before, all except one of your mandatory fixes have been done, so the bus resistors are 2.2K as per your information.

I had two different MC68000 CPUs, and both of them were causing issues with the relocator.

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Re: Mega ST project

Post by stephen_usher » Mon Oct 18, 2021 2:18 pm

How many layers is that relocator?

Given my experience, without discrete power and ground planes the 68000 will generate so much noise on the power and ground rails that it will start missing clock cycles at the very least. The HC will be lower power and hence will probably generate smaller power spikes.
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Re: Mega ST project

Post by exxos » Mon Oct 18, 2021 2:33 pm

stephen_usher wrote:
Mon Oct 18, 2021 2:18 pm
The HC will be lower power and hence will probably generate smaller power spikes.
That is not exactly true.. CMOS inputs tend to be more capacitive will actually generate higher spikes, but the overall current would be less than TTL for example. So CMOS tend to oscillate more, and is compounded by bad grounding. Despite its overall current consumption being less than TTL.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~

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HigashiJun
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Re: Mega ST project

Post by HigashiJun » Mon Oct 18, 2021 2:43 pm

stephen_usher wrote:
Mon Oct 18, 2021 2:18 pm
How many layers is that relocator?

Given my experience, without discrete power and ground planes the 68000 will generate so much noise on the power and ground rails that it will start missing clock cycles at the very least. The HC will be lower power and hence will probably generate smaller power spikes.
The relocator is 2 layers only.

I really do not know why everything is OK now, but the most important is that it do work.

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HigashiJun
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Re: Mega ST project

Post by HigashiJun » Tue Oct 19, 2021 2:12 pm

Had some time today to test my setup further.

I could launch programs from the HDD, FDD and USB without a single issue.

Writing to these devices also worked without a glitch.

So the MC68HC000 definitely cured my MEGA ST issues with the relocator. :)

(Just to check if I also could make Exxos' 16MHz ST booster rev. 1.4 work, I tried to swap its CPU with the MC68HC000 but it was a no go and I only had a black screen...).

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HigashiJun
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Re: Mega ST project

Post by HigashiJun » Wed Oct 20, 2021 10:02 am

Just a new idea for my project.

I had an old slot-in DVD multi drive (Matsushita UJ-875) laying around so I decided to use it in my Mega ST.

When I first installed the drive, I realized it was set as MASTER.

As I also want to use an SSD drive later, which has to be set as MASTER, I had to turn my DVD multi drive into a SLAVE device.

After a little and simple mod, the result is as expected and HDDriver recognizes now the unit as a SLAVE device (though the drive appears with a weird name).

DVDmulti.jpeg
DVDmulti.jpeg (326.29 KiB) Viewed 127 times

As this is a slim drive, I should be able to pack it somewhere in the Mega ST, even if I have to make a cradle for it.

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JezC
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Re: Mega ST project

Post by JezC » Wed Oct 20, 2021 1:44 pm

Looks like the device name has been byte-swapped?

Really good result that it's recognised & working though!

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