[OTG on 'L476] What is OTG_FS_NOE?

[waclawek.jan]

Posted on October 06, 2017 at 10:56

I can't find any indication in DS/RM, what OTG_FS_NOE pin might be good for.

Please, explain.

Jan Waclawek

[Khouloud GARSI]

Posted on October 27, 2017 at 17:51

Hello Jan,

OTG_FS_NOE = USB FS OTG Output Enable (active low).

This point is highlighted internally and the explanation above will be added to our documentation.

Khouloud.

[waclawek.jan]

Posted on October 27, 2017 at 19:06

OK so I guess this is the output to control the 5V power switch/charge pump/step-up, to provide 5V VBUS for the attached device in Host mode (or if set to be OTG A-device).Correct?

So how exactly does it work? What exactly controls its state?

IMO, answers to all these questions ought to be added to RM, and Figs.494..496 updated acordingly.

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Is this feature available also on other STM32, e.g. the STM32F446, which has a newer version of the OTG core?

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I looked also into Cube whether I can find usage cases: in the 'L476 EVAL, the VBUS switch is controlled by a different pin (i.e. has truly be GPIO); 'L496 Disco has this switch controlled by the slave mcu; and for the 'L476 DISCO, where it's controlled by PC9 which is also said to be OTG_FS_NOE, there's no host nor OTG example in Cube...

JW

[Khouloud GARSI]

Posted on November 07, 2017 at 18:12

Hi Jan,

OK so I guess this is the output to control the 5V power switch/charge pump/step-up, to provide 5V VBUS for the attached device in Host mode (or if set to be OTG A-device).Correct?

-> In fact, it's the USB FS OTG

D+/D- data line

Output Enable. So this is nothing to do with enabling VBUS (which is rather treated as an input on the STM32 MCU: section “Host port power' in the reference manuals explains that we do not handle the generation of VBUS).

Is this feature available also on other STM32, e.g. the STM32F446, which has a newer version of the OTG core?

-> This feature is available on STM32L4 devices.

Khouloud.

[waclawek.jan]

Posted on November 07, 2017 at 18:32

Khouloud,

Thanks. I still don't quite understand the usage:

-> In fact, it's the USB FS OTG

D+/D- data line

Output Enable.

So, if OTG_FS_DP/DM are correctly set in GPIO and I don't select the respective AF for any of the OTG_FS_NOE pins, DP/DM remains always enabled; and if I select the respective AF for one of the OTG_FS_NOE, then DP/DM are enabled only when that pin is low, correct? And if it is high, DP/DM goes Hi-Z, including all the OTG_FS-related pullups/pulldowns, correct?

Looking forward to the new DS+RM appearing soon, and explaining this in detail ;)

Jan

[Khouloud GARSI · Accepted solution]

Posted on November 09, 2017 at 15:59

Hi Jan,

• The NOE pin is only an output showing the current state of enable of the DM and DP lines. Programming AF (concerning NOE) will not in any way change the behavior of DM and DP pins.
• After verifying, this feature is also available on STM32F0 and STM32L0 devices.
• I have already reported this point internally and an explanation will be provided on our documentation.

Khouloud.

[waclawek.jan]

Posted on November 09, 2017 at 16:02

Thanks for the details, Khouloud.

Jan

[Khouloud GARSI]

Posted on November 09, 2017 at 16:05

You're always welcomed!

Khouloud.

[Georgi Marinov]

The output enable control signal of the analog transceiver (active low) is provided externally

on USB_NOE. It can be used to drive some activity LED or to provide information about

the actual communication direction to some other circuitry.