I've seen bidirectional "bus switch" type chips, before... but in my experience they've generally been found to be quite slow... Plausibly, I was somehow stuck on something like the 4066, which wasn't really designed to switch data, but analog/audio?

Needed to switch out my 5V old TTL chips with 3.6V compatibles; it's time to eliminate variables. Again, 'scoping my 5V logic running at 3.6V shows they seem to be doing their job, but there are some atypically (for me) timing-critical aspects in this project, so maybe the lower-than-spec'd-voltage is causing slower propagation-delays, etc...

(I'm saying: From-experience: Don't be intimidated to use 74xx 74Sxx 74LSxx chips, maybe even the 74Fxx, in 3.6V circuits, if you're not worried about timing or doing something too complex (or professional). Seriously, I've been using these 5V chips from the 1970's/80's in various 3.6V circuits for a couple years, now... It's certainly worth a try if it's all you got!)

That said, it's time to eliminate variables, and this one-shot circuitry is pretty complex, in comparison to other such TTL-limit-stretching circuits I've done.

THAT said, Keep your old motherboards and old-dead PCBs from things you take apart. I've got more than I should, probably, but with four boxes (20+ years of taking broken things apart), I can usually find just about any common-enough component I need, or something similar-enough to do the job. This time, a bunch of 74HC-series would come in handy...

And low-and-behold, there's an old Pentium 166 laptop's motherboard in the top of the top box. Littered with 74HC chips, as well as others that could come in quite-handy some day...

AND easily a half-dozen "CBT3384"s on just one side of the board... Didn't know what they were, but there were so many it was worth looking up. This is a game-changer, here. That's the SN74CBT3384A, from TI. And, basically, it's a high-speed bidirectional bus-switch. Bidirectional, in this case, NOT requiring a direction-change control-signal. Handy for AVR IOs. Propagation-delays of ~0.25ns. (I've never even seen a Tpd < 1ns in *any* chip, before). This thing looks Quite Handy. And I've got *a lot* of them.

I've already a bunch of ideas where they could be used... partially from exploring *now that I have 'em* but also from numerous previous designs where I thought "yahknow what'd be nice..."

Here's a quick idea: You've got a bus with a parallel FLASH chip, and a parallel SRAM, they both share the same I/Os for data, on the AVR... (Bidirectional). Now, say they're both a little slow, so enabling/disabling the output on one may take several AVR clock-cycles. Throw a bus-switch between each and the bus, and you can set-up a read from the flash, and while waiting for it to retrieve the data, also do a write to the SRAM...

It's just one idea. These things are, allegely, SO fast they could be used in all sortsa switching-environments nearly completely invisible to the peripherals... I dunno, maybe use that SPI port to read/write to an SD-card, and switch the bus over to something entirely different...

Or, in the case of this "logic analyzer": use them to switch the sample/repeat mode, or who knows. It's not perfect for this system, as-designed, but I likely would've designed it differently if I'da known I had these. (Though, I was originally trying to keep it as simple as possible, with as little external logic as possible, so who knows). Either way, they definitely are going in the Useful Tools category. And, despite their tiny-spacing, I've managed to figure out a way to put 'em on bigger-spacing breakout-boards without much difficulty (sacrificing 4 switches in the process, but not bad considering they have 10).

So, there's that.

Other useful things I've found in large-quantities on old dead laptop-motherboards: high-current P-Channel MOSFETs, which are excellent for power-switching. And despite their SMD footprint, because they share so many pins for the same purpose they're pretty easy to use on regular breadboards, or even just attach some big-ol' wires, and heatshrink for prototyping...

As far as the project goes... I've done write/read, and have gotten some weird results. Thus soldered-up these 74HC's to replace the 74S's. We'll see where this goes.

I might as well rename this project from "mishmash" to "sdramThing3.5", since the original mishmash of project-ideas has been put on hold for so long... Ah well.