What's in an USB-C cable?

[uliano]

I just received this  ch32v307 evaluation which has an onboard debugger driven by an USB-C connector (on the right, the two on the left are for appliactions). Nice, I thought, I just happen to have (quite) a few USB-C to USB-C cables it would be nice to connect directly from my MacBook to the board!

Alas no! It didn't work directly with any of those cable (and I tested them all!) and I tested both on the MacBook and a Thinkpad.

It works only using an USB-A to USB-C cable either directly (on the Thinkpad) or through an adapter USB-A to USB-C then chained with the USB-C to USB-C cable.

I'm puzzled and also I expected technology and progress would have done (way) better.

[Berni]

The problem is the extra CC pins on USB-C that inform the device about how to handle what was just plugged in.

These modern small laptops use the USB-C for both charging and to connect devices, so the port has to know if it has to receive power or give out power, if so at what voltage. They also tell it to interrupt the power when the cable is pulled out, since at the higher power levels this could draw an arc and damage the connector.

USB-A does not have these extra pins so 5V power is always presented by the host. So a USB-A to USB-C cable will provide power even when the USB-C end is not plugged into anything. However on a USB-C to USB-C cable these pins are wired directly between both ends. In the case of a USB-C to female USB-A adapter cable, the appropriate resistors are built into the cable, this tells the host machines USB-C port "Please act like a USB host and provide 5V power".

So now the device on the other end has to present the correct signals/pullups/pulldowns in order to tell the host to provide power. So there are some badly designed devices out there that just use a USB-C connector as a direct replacement for a microUSB, only connecting the regular USB 2.0 pins.

[uliano]

I'm starting to suspect that R10 and R11 could be soldered in order to request power... If only I had the schematics

[uliano]

and here it is

So, does this means that i need to solder 5k resistor and it will power the board?

[uliano]

Easy! 

[argile_tile]

https://www.extremetech.com/computing/115251-how-usb-charging-works-or-how-to-avoid-blowing-up-your-smartphone

all c cables are not alike despite labeling.  be careful.  a separate url has lists of "good and bad" cables - which is "out of date" unfortunately.

[newbrain]

If only I had the schematics

The github fairy granted your wish.
Bottom right corner.

Strange that you did not know of openwch github repos?
https://github.com/openwch/ch32v307

EtA: Ah, should have read all the messages