03:59 <balrog> has any work been done so far for Altera MAX CPLDs (specifically EPM7032)?

05:02 <kc8apf> There was some work done on MAX V but not the original MAX

06:42 <rvense> balrog: one thing i've been sort of looking into recently is that there appears to be some sort of link between the atf1508 and the epm7128. atmel have a tool that converts files for the epm part to ones that work for the atf part

06:43 <rvense> i don't know whether the inverse is possible, but i'm currently waiting for some hardware to try it out

06:47 <rvense> http://ww1.microchip.com/downloads/en/AppNotes/DOC0916.PDF

20:43 <pie_> obviously I dont really understand the physics of this, if a USB serial adapter exposes ground from the usb port, can I leave the battery in the battery powered device I want to talk to, and connect ground to the negative pole of the battery?

20:53 <rvense> pie_: i may not be fully understanding what you're describing, but isn't that what happens when you plug a phone into a computer via usb?

20:54 <pie_> rvense: I guess. But I imagine in that case they may have designed that to work? I don't know.

20:55 <pie_> rvense: attempting to clarify: I have a battery powered device. The serial thingy has ground and power and signal pins. The question is how can I hook up the serial probes without removing the battery.

20:56 <pie_> It was suggested to me earlier that it should be sufficient to connect ground and the data lines.

20:58 <rvense> yes, i think so to. i've done as much before. i definitely would not connect the power lines.

21:00 <pie_> I wasn't planning to, I'm just not sure how the ground stuff would work. My intuition says the battery is sort of floating in the void and hooking up ground puts it at some arbitrary absolute position, and the positive pole is then relative to that, so it seems sensible. - but that also seems a little weird.

21:01 <pie_> Im assuming connecting only the data lines won't work because then it doesn't have a reference.

21:03 <zyp> correct, you need a common ground as a reference

21:09 <pie_> Ok well I did the stuff and nothing has exploded yet.

21:10 <pie_> Thanks.

21:17 <pie_> Now I just need to find something I can leave this plugged into and figure out how to do usb over ethernet, and then I can work on debugging it without having it dangling off my machine all the time.

21:22 <rvense> pie_: my understanding is the same as yours. it also makes me a little uneasy and would prefer if "ground" was something more fixed.

21:23 <rvense> i'm wondering now if it'd work to connect only the power lines. if you've got 5v circuits on both sides, that would also create a close enough common reference, kind of?

21:25 <rvense> i think the problem with connecting both power is that you've then got two power supplies connected, and if they're a little off from each other (if they're not exactly 5v), then you get current flowing from one power supply into the other, and that's Bad

21:26 <pie_> yeah im just thinking about backflow in one direction or the other

21:26 <pie_> discharging the battery is bad

21:26 <pie_> charging the battery is bad

21:26 <rvense> but... i'm not going to try it and see

21:26 <pie_> oh yeah thats what you just said

21:27 <rvense> except i don't know fancy words like backflow :)

21:31 <pie_> I just made that up

21:34 <rvense> .. oh

21:36 <agg> the only alternative to connecting the grounds is to make a fully isolated interface (e.g. you could imagine the battery-powered device lighting an LED which the computer side detects with a photodiode, no electrical connection required), which is sometimes done if you really want to not connect things electrically

21:36 <agg> for example, ethernet is isolated (using transformers), so the grounds aren't connected, and it provides some useful properties when you run ethernet cables between buildings or over long distances

21:37 <agg> if you had a battery powered oscilloscope, one use case is being able to measure things without a ground reference (for example measuring one battery in a high-voltage pack without ever 'seeing' any high voltages), so then the oscilloscope might want its usb interface isolated

21:37 <agg> for a very high precision device you also might want to avoid connecting the grounds because conducted noise can cross over

21:38 <agg> (read 'very sensitive' where I wrote 'very high precision')

21:38 <agg> but for a standard battery powered thing like a phone or some widget, connecting usb ground to the battery -ve is the standard normal thing, and doesn't cause any issues

21:40 <agg> (and your understanding of the physics is correct, the disconnected battery only has a potential difference across its two terminals and is floating with respect to the computer, but if you then attach the grounds their signals all have a common reference - but just connecting the grounds first doesn't cause any current to flow* because there's only one conductor)

21:40 <agg> (*except for ESD discharge currents, which you do sometimes have to watch out for, and is why often connectors make sure ground connects before data, for example USB-A having longer power contacts and shorter data contacts)

22:27 <pie_> Hm. Looks like it might not be happy without the common vcc sometimes. Not sure.

22:28 <pie_> agg: thanks for elaborating!

22:28 <pie_> another everyday-ish example is sata cables