4 ms·

That's close, but it's not quite complete. There seems to be lots of confusion here, and that's natural: It is confusing. For just-getting-power from a USB A

by ssl-3 4mo ago

That's close, but it's not quite complete. There seems to be lots of confusion here, and that's natural: It is confusing. For just-getting-power from a USB A port into a USB C peripheral: There are supposed to be 2 resistors in the peripheral device [always], and also 1 resistor within the cable for USB-to-legacy cables[1]. That's 3 resistors, total, to get a relatively dumb USB-C equipped peripheral device to reliably charge from both USB A and USB C hosts/chargers/whatevers: The cable itself: It gets an internal 56k pullup resistor between Vbus and USB C pin A5 -- which is the CC line [yes singular]). This resistor signifies the capabilities of the host/charger/whatever for devices that care (some do care, some do not care). The peripheral: This minimally needs two pulldown resistors [commonly 5.1k], between each of CC1 and CC2 [yes a plurality] and ground[2]. This tells a compliant USB C host/charger/whatever "It's OK! Send the juice juice!" regardless of connector orientation. [1]: https://www.usb.org/sites/default/files/USB%20Type-C%20Spec%20R2.0%20-%20August%202019.pdf https://www.usb.org/sites/default/files/USB%20Type-C%20Spec%... section 3.5 [bleh]: Again, it is a confusing thing. Nobody said that dealing with such flexible, ambidextrous connections would be simple. CC performs a lot of different tasks: It can be a bidirectional serial bus for active PD negotiations, and/or a resistor network for passively dealing with power, and it's the bit that performs detection of cable orientation for applications where that matters, and it probably does other stuff too. That single little wire is clever AF. It'd be simpler to use multiple wires instead of just one, but that would take more copper. Copper is expensive, and we each save a tiny bit of money (or a large pile of money globally) by using less copper instead of more of it.

exmadscientist 4mo ago
My point, which matches what you've written out in more detail, is that there's supposed to be stuff (resistors) in the cable, stuff which is often not there. There are plenty of these abhorrent cables in the wild. And when you come across one, things get weird, because some sources and sinks deviate from the standard in ways that make them work with these bad cables. Others don't do that. (I believe there were a lot more abhorrent cables in the early days, and thus began the chain of accommodation....) So unless your cable is known-good, if you are having trouble, trying a different cable should be the first thing you do. It really does often get things working. Contrarily, if you have identified a naughty cable, it should be immediately widlarized.
- ssl-3 4mo ago
  I gathered that you knew that. I'm mostly just trying to complete the picture for those following along at home, who might find some of this resistor business to be a bit weird compared to the USBs of yore. Except the old ways were weird in unseen ways, too. Some combinations of cable, phone, and charger worked well and some barely worked at all. We're in much better shape with USB C and PD. It's generally a good, forward-looking way of doing all kinds of things. I just wish the cables and ports were better-marked, and that manufacturers stopped fucking around by making non-compliant stuff, and that there were a clear way with two battery-equipped USB C devices to unequivocally declare that a particular one will charge the other (and not the other way 'round). And yes: The non-compliant widgets should ideally be named, shamed, and Widlarized -- not simply tolerated or worked around.
- SAI_Peregrinus 4mo ago
  Resistors don't go in the cable. They go in the device. They indicate that the device can't negotiate voltages above 5V, so just send 5V. USB-A has no ability to provide voltages other than 5V, so there's no need for indicating it's the max. Not all chargers have USB-A ports. Many laptops don't have USB-A ports, so if you want to charge a noncompliant device from a laptop it won't work. Or a laptop charger, which is dedicated USB-C.

by ssl-3 4mo ago

exmadscientist 4mo ago

My point, which matches what you've written out in more detail, is that there's supposed to be stuff (resistors) in the cable, stuff which is often not there. There are plenty of these abhorrent cables in the wild. And when you come across one, things get weird, because some sources and sinks deviate from the standard in ways that make them work with these bad cables. Others don't do that. (I believe there were a lot more abhorrent cables in the early days, and thus began the chain of accommodation....) So unless your cable is known-good, if you are having trouble, trying a different cable should be the first thing you do. It really does often get things working. Contrarily, if you have identified a naughty cable, it should be immediately widlarized.

ssl-3 4mo ago
I gathered that you knew that. I'm mostly just trying to complete the picture for those following along at home, who might find some of this resistor business to be a bit weird compared to the USBs of yore. Except the old ways were weird in unseen ways, too. Some combinations of cable, phone, and charger worked well and some barely worked at all. We're in much better shape with USB C and PD. It's generally a good, forward-looking way of doing all kinds of things. I just wish the cables and ports were better-marked, and that manufacturers stopped fucking around by making non-compliant stuff, and that there were a clear way with two battery-equipped USB C devices to unequivocally declare that a particular one will charge the other (and not the other way 'round). And yes: The non-compliant widgets should ideally be named, shamed, and Widlarized -- not simply tolerated or worked around.
SAI_Peregrinus 4mo ago
Resistors don't go in the cable. They go in the device. They indicate that the device can't negotiate voltages above 5V, so just send 5V. USB-A has no ability to provide voltages other than 5V, so there's no need for indicating it's the max. Not all chargers have USB-A ports. Many laptops don't have USB-A ports, so if you want to charge a noncompliant device from a laptop it won't work. Or a laptop charger, which is dedicated USB-C.