iMX8M Plus: How to enter USB Download Mode?

[cdvd]

After configuring the boot pins to USB Download Mode, what other requirements are there to enter the mode? What should the state of the VBUS pin be, if relevant?

I have tried entering USB download mode using my PHYTEC devboard but couldn't and I need to make sure it works on a board I'm designing.

Thanks!

[riteshmpatel]

Hi @cdvd,

I hope you are doing well.

USBx_VBUS shall be powered by 5V. One can check the input voltage range of the USBx_VBUS pin in the i.MX8MP datasheet.

One can also refer to Section 6.1.2.3 Boot From Fuses mode in the i.MX8MP Reference Manual.

Thanks & Regards,
Ritesh M Patel 

[cdvd]

Hey @riteshmpatel,

I've looked at the reference manual, and the section about booting from fuses doesn't talk about VBUS at all. 

You are saying to "power" the VBUS pin (USB1/2_VBUS_3V3) in the PHY interface, but really it should be pulled to a voltage. Previous releases of the iMX series had a power requirement at this pin, but the 8MP does not.

My question is, what should the connection here be to make sure USB works on OTG mode?

Please find screenshot from your reference design, saying that "VBUS can ignored if not using OTG mode". But what if OTG _is_ required?

Moreover, when looking at "production programming pins", you are exposing both USB_DM and USB_VBUS. So VBUS must be required for OTG, right? Why else would you do this?

What are the USB VBUS pin requirements for OTG, if any? Do I need to connect it to the USB connector's VBUS? How, if the connector can be powered by the board itself via a power switch? 

Thank you!

[riteshmpatel]

Hi @cdvd,

If one wants the USB to work in OTG mode, the USBx_VBUS pin needs to be supplied with a voltage range listed in the datasheet. Please note that for i.MX8MP, USBx_VBUS is not the power pin, rather it is a sense pin.

One can refer to the EVK schematic for connection reference of the USBx_VBUS pin.

Thanks & Regards,
Ritesh M Patel