[EE]:: Chromebook psu cable colours / functionality
Locked
Re: [EE]:: Chromebook psu cable colours / functionality
 
|
> Voltage selection for various 5V/ XA ratings is typically by resistor magic. Are you sure? I thought older USB was via resistors, but that the new USB-C stuff involved software-level negotiation, sort-of like PoE. BillW -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
Re: [EE]:: Chromebook psu cable colours / functionality
|
|
>
> I thought older USB was via resistors, but that the new USB-C stuff involved software-level negotiation, sort-of like PoE. Since I now have a charger of my own to fix, I investigated this more thoroughly. Negotiation IS required to get the higher voltages/higher power delivery, but it uses a separate (non-USB) conversation on the CC signal. CC signaling is WRT the GND connection. (This is different than the 4-wire V+/GND/DM/DP scheme, where pull-up/down resistors on the data lines would mean ‘something.’) A three-wire power-supply-only cable is “extremely likely” to consist of V+ (red), GND (black), and CC (blue, in my case?) Pretty nice presentation: https://web.archive.org/web/20161220102831/http://www.usb.org/developers/presentations/USB_DevDays_Hong_Kong_2016_-_USB_PD.pdf <https://web.archive.org/web/20161220102831/http://www.usb.org/developers/presentations/USB_DevDays_Hong_Kong_2016_-_USB_PD.pdf> CC also apparently controls the “alternative pin function switching” and perhaps “other stuff”, so the protocol used is relatively complex. (Assuming that everything is actually conforming to the USB 3.2 specs…) Sigh. Rant: Back in the bad-old-days, computers were connected with rs232, and if you had a problem, it was practically “always the cable.” Wrong gender on one end or the other, wrong DCE/DTE-ness somewhere (crossover or not), not all necessary signals were actually connected from one end to the other (cables varied from 3 to 26 conductors), etc. USB came along to fix all of that. ONE standard cable with obvious “host” and “device” sides. It was all good up until USB3. And now we have to worry about connector types on each end, how many signals are actually implemented in the cable, and even whether the wires are thick enough. Progress :-( BillW -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
Re: [EE]:: Chromebook psu cable colours / functionality
|
|
On 2021-01-26 16:38, William Westfield wrote: >> I thought older USB was via resistors, but that the new USB-C stuff involved software-level negotiation, sort-of like PoE. > Since I now have a charger of my own to fix, I investigated this more thoroughly. > Negotiation IS required to get the higher voltages/higher power delivery, but it uses a separate (non-USB) conversation on the CC signal. CC signaling is WRT the GND connection. > (This is different than the 4-wire V+/GND/DM/DP scheme, where pull-up/down resistors on the data lines would mean ‘something.’) > > > A three-wire power-supply-only cable is “extremely likely” to consist of V+ (red), GND (black), and CC (blue, in my case?) > > Pretty nice presentation: > > https://web.archive.org/web/20161220102831/http://www.usb.org/developers/presentations/USB_DevDays_Hong_Kong_2016_-_USB_PD.pdf <https://web.archive.org/web/20161220102831/http://www.usb.org/developers/presentations/USB_DevDays_Hong_Kong_2016_-_USB_PD.pdf> > > CC also apparently controls the “alternative pin function switching” and perhaps “other stuff”, so the protocol used is relatively complex. (Assuming that everything is actually conforming to the USB 3.2 specs…) > > Sigh. Rant: Back in the bad-old-days, computers were connected with rs232, and if you had a problem, it was practically “always the cable.” Wrong gender on one end or the other, wrong DCE/DTE-ness somewhere (crossover or not), not all necessary signals were actually connected from one end to the other (cables varied from 3 to 26 conductors), etc. USB came along to fix all of that. ONE standard cable with obvious “host” and “device” sides. It was all good up until USB3. And now we have to worry about connector types on each end, how many signals are actually implemented in the cable, and even whether the wires are thick enough. Progress :-( > > BillW If useful, by far the best video I've ever seen to quickly describe how 'fun' USB charging is: https://youtu.be/1nx_n-wEtII -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist |
«
Return to MicroControllers - PIC
|
1 view|%1 views
| Free forum by Nabble | Edit this page |