How use usb data line without usb core

RE: How use usb data line without usb core

Jakub Oller — Wed, 13 Nov 2019 21:43:05 GMT

Thanks!

RE: How use usb data line without usb core

Turbo J — Thu, 07 Nov 2019 01:30:37 GMT

The D+/D- pins will not be powered - which is not the same as high impedance. According to PS description, the PHY with the data pins is powered from VBUS via USB LDO.

Which means you cannot share these pins in a connector - the unpowered USB pins would act as (sort of) pull downs and might reverse-power the USB PHY because there are probably diodes from the pins to he voltage rail at DECUSB.

RE: How use usb data line without usb core

Jakub Oller — Wed, 06 Nov 2019 23:21:17 GMT

Hi,

I have the same exact question and I can see that it has not been fully answered yet.

I want to have a single connector for either USB or GPIO depending on VBUS voltage (we will use USB if VBUS is present, GPIOs if VBUS is at 0V or floating). The question is: what happens (electically) to D+ and D- pins when VBUS is at 0V or floating? Are they high impedance?

RE: How use usb data line without usb core

Vlad Mokhnachov — Thu, 22 Jun 2017 14:10:07 GMT

RK, You are fully right.

RE: How use usb data line without usb core

Jørn — Thu, 22 Jun 2017 13:33:03 GMT

Ah yes of course, I believe you're right. I will look further into this.

RE: How use usb data line without usb core

RK — Thu, 22 Jun 2017 12:24:40 GMT

so I finally, after the comment from yesterday, understand what they are trying to do. They aren't trying to use GPIOs for USB. What they're trying to do is have one connector on the board, a USB connector, but have it work both for USB (usual case, usual wiring) or I2C (with some custom connector). So they have D+/D- on the connector hooked up to D+/D- pads on the chip but also to two GPIOs for when they're using the USB connector for I2C. I think what they hoped for /expected is that if the USB module itself is off, the D+/D- pads would be high impedence and wouldn't interfere with the I2C communication going into the GPIO pins. I assume when using USB,they set the GPIOs high impedence and that works. So I guess the question here is what are the electrical characteristics of the D+/D- pads when the USB module is turned off?

RE: How use usb data line without usb core

Jørn — Thu, 22 Jun 2017 11:24:53 GMT

Hello Vlad

As RK has stated none of the GPIO of the nRF52840 supports USB, and the USB pins are exclusively used for USB. So if you want to use the GPIO for USB do that you would have to bitbang it somehow, though I'm not sure if that would be possible.

Unfortunately we do not have any examples or reference code for something like this. I have seen people claim to have bitbanged USB on ARM M0 processors, however for our products you would have to worry about the SoftDevice using part of the processor time as well.

To my knowledge USB has never been bitbanged on any of our products, so I'm afraid I don't have any further advice on how to achieve something like that.

Best regards

Jørn Frøysa

RE: How use usb data line without usb core

Vlad Mokhnachov — Wed, 21 Jun 2017 13:58:07 GMT

We want use usb connector for usb and for i2c.

First case: connecting board to usb host via usb

Second case: connecting board to another board via i2c

Both case used one usb connector(GND, VCC, D+ and D-), but for i2c D+ changed to SDA and D- to SCL.

RE: How use usb data line without usb core

RK — Wed, 21 Jun 2017 13:35:56 GMT

What do you mean you have "connected gpio pins to USB pins"? The circuit diagram makes it look as though you've connected USB D+ both to the D+ pin and to a random GPIO. Why have you done this? The D+/D- pins can only be used for USB and nothing else and no other GPIOs can take a USB signal so it's hard to understand what you're trying to accomplish.