exxos's Atari, Amiga & retro forum

My latest project requires me to sniff CPU writes to the data bus.

I was hoping to have a no-soldering-required design so made a beeline for the (normally socketed) shifter chip and have placed an interposer board there.

In my gleeful machinations, however, I overlooked that the shifter sits on the DRAM side of the great memory divide (the four buffer chips that isolate the actual DRAM memory from the CPU data bus when the video circuitry is doing its thing).

So, my question for the learned followers of the forum: where can I best sniff (all 16 lines) of the databus that would either:

1) not require any soldering on behalf of the installing party;
or, at a push
2) only require soldering, definitely no desoldering.

Things that have crossed my mind:

* ROM sockets.

They're 8 bit so it'd need at least two interposers.
Clearance on some motherboards may be an issue with an interposer and then the ROM chip.
Lots of people have TOS switchers or similar installed already.

* Make a little hat for some chip(s) that could be soldered on top.

Requires some soldering.
Inelgant.
Might need a few goes to get right.
Would it interfere with other addons?

* Resistor pack interposer

Desoldering. Ugh.
8 bit again.
Locations perhaps awkward.



Are there any other routinely-socketed chips on the Pre-STE range which I'm kind of targetting?

BW

@Badwolf, what about using the cartridge port. Just create a breakout PCB for the data lines.

Soldering is generally the default :( The "best" likely place to sniff is the blitter socket. Otherwise it probably have to be a CPU breakout. ROM may work like you say, but space is limited and later STFM revisions have the ROMs soldered in anyway.

Or use a H5 as its designed for easier upgrades and everything is in sockets ;) :hide:

Icky wrote: 29 Apr 2025 14:34 @Badwolf, what about using the cartridge port. Just create a breakout PCB for the data lines.

I had been casting furtive glances at that, but the rest of the project is internal and there a few popular cartridge port addons these days meaning I'd have to provide a pass-through or something.

Ta, though.

BW

exxos wrote: 29 Apr 2025 14:36 Soldering is generally the default :(

Bah. I feared as much.

The "best" likely place to sniff is the blitter socket. Otherwise it probably have to be a CPU breakout. ROM may work like you say, but space is limited and later STFM revisions have the ROMs soldered in anyway.

Ah, I forgot to mention that the blitter socket may be somewhat obscured already. That may be another issue :P

Or use a H5 as its designed for easier upgrades and everything is in sockets ;) :hide:

Plan for the worst case: makes the best case easier! :lol:

BW