How does PA9 (USB VBUS Pin) detect connection by devices?

[StephanMair]

Posted on April 16, 2014 at 03:34

I understand it is used to detect whether a device is connected or pulled out. But I have no idea how.

So my questions are as follows:

1,How exactly does that pin work?

2,I can use whatever pin that is five tolerant to provide power supply for my devices (my STM32 is working at host mode of course) right? And I can even use 2 or even 3 of them soldered together to provide power, right?

[chen]

Posted on April 16, 2014 at 10:32

Hi

''And I can even use 2 or even 3 of them soldered together to provide power, right?''

Absolutely NOT!!!!

If you need to provide power, use a USB interface device. They are designed to provide power and limit current.

The STM32 has an absolute power/current output (for all IO pins summed together) limit.

It is no where near the 500mA that USB requires.

''1,How exactly does that pin work?''

http://www.beyondlogic.org/usbnutshell/usb2.shtml#PowerVbus

[StephanMair]

Posted on April 17, 2014 at 12:19

Hey many thanks. I read it somewhere that GPIO pins could be used to provide power but clearly I'm mistaken here. Silly me.

I'm reading the article you posted. I've been reading on and off that site for quite some time now, but didn't go through it thoroughly.

Thanks.