exxos's Atari, Amiga & retro forum

frank.lukas wrote: 17 Aug 2025 08:49 The Mega ST Bus is not only a 1:1 mapping from the 68000 CPU Signals. However some Mega ST bus cards often use only 68k CPU signals but not all. The Mega ST Bus has no VCC connections.



mst_bus.jpg

You beat me to it, I have some megabus IDE adapters and they require a separate 5v connection because of this.

rubber_jonnie wrote: 17 Aug 2025 09:06

frank.lukas wrote: 17 Aug 2025 08:49 The Mega ST Bus is not only a 1:1 mapping from the 68000 CPU Signals. However some Mega ST bus cards often use only 68k CPU signals but not all. The Mega ST Bus has no VCC connections.



mst_bus.jpg

You beat me to it, I have some megabus IDE adapters and they require a separate 5v connection because of this.

The adapter I made has headers on it for all of the missing signals.

PhilC wrote: 17 Aug 2025 09:33

rubber_jonnie wrote: 17 Aug 2025 09:06

You beat me to it, I have some megabus IDE adapters and they require a separate 5v connection because of this.

The adapter I made has headers on it for all of the missing signals.

Good stuff

I'll be interested to hear how this goes...

One of my Mega's has the ATW900/2 installed but the other has the Megabus connector obscured by the strange memory expansion board, so a long-term plan is to replace the memory expansion with one that will allow me to use the Megabus.

Once I've got that far, this might be one of several contenders for what goes in the Megabus...

I must look for the opposite (68k DIP to Megabus adaptor) at some point as then options like the ATW800/2 and an accelerator mounted in an H5 might be possible...

This has got me wondering...although it would probably be 'nigh impossible',
because of the usual space constraints but...

The STacy does have an unused megabus connection on it's motherboard.

Some very early models actually had the port to the outside but that was
dropped and most just have the place for it on the motherboard, without
even a header.

PS I've been waiting for some adventurous (crazy?!) soul to look at putting
the Mega ST version of the ATW800/2 transputer board in one... :lol:

The Atari Stacy has a full MegaST Bus. You need a Male 72pin A-B-C Connector DIN 41617 and a 64pin Male Connector A-B DIN41617 and a Female 72pin A-B-C Connector DIN 41617 on the Atari Stacy Mainboard ...

frank.lukas wrote: 17 Aug 2025 18:12 The Atari Stacy has a full MegaST Bus. You need a Male 72pin A-B-C Connector DIN 41617 and a 64pin Male Connector A-B DIN41617 and a Female 72pin A-B-C Connector DIN 41617 on the Atari Stacy Mainboard ...

So Frank, I gotta ask - do you honestly think that it's "do-able"?

I was half-kidding when I made that post because of the tight
spaces in the STacy. :)

You can do that and use an ATW800/2 externally. So, just solder the female header into the Stacy and solder a piece of external cable together, connecting the male header to the Stacy and the male header of the MegaST bus connector. The whole thing shouldn't be too long and should work. Otherwise, you could install a PuPla/2 in between to buffer the signals. I've had good experiences with a long Mega ST bus connection.


... and you can Print a nice 3D Print case for that. Try it ...

Female and Male 72pin A-B-C Connector DIN 41617 can be hard to find. In Germany by Reichelt there are only 64Pin ones and more but not 72Pin ones ...

Ah, okay - externally. Gotcha.

Add a 3D printed case for the ATW800/2 and it could
still be made to look clean and neat as well.