exxos's Atari, Amiga & retro forum

Evening All,

So todays task, start the process of trying to get a TF536 to work on my Mega ST.

As standard the TF536 won't boot with my Mega. It asserts a 50hz screen but gets no further. Both the /HALT & /RESET work as they should but the whole thing comes to a grinding halt.

Taking a look at the 8mhz waveform I decided to try adding a 100pf cap between the CLK and 5v directly on top of the cpu. This makes the Mega boot to the Atari Fuji but bombs on 11 bombs, so ive made a bit of progress. Just wondering what to try next.

Waveform without cap
And waveform with 100pf cap to 5v
I'm going to scope out a few other things when I get time over the next few days but wondered if you guys have any tips please.

100pF on DTACK ? I had to add 50pF to get mine to boot on my H4.. Plus you need to do "the usual fixes" as well.

exxos wrote: ↑Mon Jul 20, 2020 9:33 pm 100pF on DTACK ? I had to add 50pF to get mine to boot on my H4.. Plus you need to do "the usual fixes" as well.

Believe it or not I've actually done the usual fixes. I tried 100pf on stack but made no difference. I have found that removing the 100pf from 5v to CLK and putting it on GND instead makes for more consistent appearance of the Fuji and bombs.

With the 100pf between CLK and GND the DTACK clock and CLK seem to sync pretty well but I'm no expert.

The clocks on the MEGA are really bad, its why I ended up designing the MEGA buffer board.

Have a look at the bottom of the page..

https://www.exxosforum.co.uk/atari/last/ ... /index.htm

@exxos i changed the five SILS to 2.2k a couple of weeks ago but this board never really played up beforehand.

This board has 120ns ram as well but when I put the pak68/3 into it last year it'd post but fail ram check.

Does this seem like a timing issue? I do need to research 68000 timings to learn more as well.

PhilC wrote: ↑Mon Jul 20, 2020 9:58 pm @exxos i changed the five SILS to 2.2k a couple of weeks ago but this board never really played up beforehand.

I'm referring to the buffer board on that page...

You could also try a 1K pullup on the 8Mhz clock to see if that helps..

@exxos you only have the one left, do you tbink this will clean up the 8mhz to the cpu socket in turn? I know it was used to take the 16mhz to the v2.2 booster originally

exxos wrote: ↑Mon Jul 20, 2020 10:07 pm You could also try a 1K pullup on the 8Mhz clock to see if that helps..

ok, will try the pull-up after work tomorrow.

Put the scope on the 030 CLK vs the 8Mhz clock.. they should be in sync and squared off until it hits fastram.