CURRENT PROTOTYPE STATUS (SEC 64MHz 68000)

[PhilC]

Sorry, I've forgotten by what was the original speed of the CPU but regardless of speed, it's an achievement to make any stable kind of increase on a chip as old as a 68000.

[exxos]

Sorry, I've forgotten by what was the original speed of the CPU but regardless of speed, it's an achievement to make any stable kind of increase on a chip as old as a 68000.

Original was 8MHz... The SEC has pretty much always run at 50MHz. The SEC itself says 20MHz on it.

[exxos]

I think I have 2.2K resistors on this motherboard (I put them in sockets thankfully so can change them easy)...

I mean 2.2K with 23 address lines , 16 datalines.. 39 pins.. 2.2K @ 5V = 0.0023A x 39 = 0.0897A. So with some other pins might as well round up to 100mA. 0.1A x 5v = 0.5watts. But of course with this thing running in MHz range, there will be RF heating aswell.

So basically if I moved to 4.7K, it should half the power going though the CPU and it may well sustain overclocking better as it will be running cooler. So I need to experiment with the pull-ups to see what I can get away with.

EDIT:
50MHz crashed after just 7 loops this time, with a heatsink on the CPU.. Something is definitely overheating somewhere.

[PhilC]

2.5 times its rated speed is pretty good :D

[exxos]

Yep.

10K's in... pretty much as expected.. Can't find 4.7K at the moment :(

IMG_4386.JPG

EDIT:

Found 4.7K.. so will leave it on for a bit before exxos powers down for the day.

[exxos]

4.7K crashed after 16 passes. I will test 4.7K again now (from cold) to see what happens. Its possible 4.7K isn't enough, or could have just been a fluke it died at 16 as it was warmed up anyway.

It seems to crash around 20 passes (about 100mins run time) but reset and its off again for another 20 passes. But of course the number isn't consistent it varies. So the crash can happen between 1 and 2 hours. I'm assuming there is some random noise on the bus causing the issue.. but with it only happening after a hour or 2, it's pretty impossible to track down where the issue is :(

Running 40MHz changes nothing either. So I can't accept its overheating, or some timing issue somewhere as it would improve with a slower clock..

I have put another 2.2K on DTACK. Possible its slow edge could be confusing things now and then.. more testing needed....

[exxos]

DTACK didn't help :(. I am currently trying 999 loops in the diagnostic cart for RAM & ROM to see if it trips up at any point.

[exxos]

I left it running YAART all night and all morning, so its had a straight 12 hour run...

IMG_4387.JPG

So its not like the booster isn't stable... :shrug:

Will load up the diagnostic cart and do a few hours of ROM checksum test see if the ROM glitches at any point...

[exxos]

It has been going about two hours now...

IMG_4405.JPG

So it is not like the ROM is un-stable either..

I will put GB6 back on see what happens...

EDIT:

Typical as it crashed on the first test :lol: :pullhair:

But the thing is, I actually change the ROM IC as I had a patched 104 which wouldn't checksum correctly in the diagnostic cartridge.. So I just put the original one back in, and the tests are running again... So next step is to introduce another wait state onto the ROM access to slow it down a fraction to see if that helps..

[exxos]

ROM 2WS

2ws.JPG

ROM 3WS

3ws.JPG

So the ROM I had issues with just, is working fine with 3WS.

So I will put back the ROM I had before, and leave it running and see what happens...