How to deal with USB pins on XL232 devices?

Technical discussions around xCORE processors (e.g. General Purpose (L/G), xCORE-USB, xCORE-Analog, xCORE-XA).
CousinItt
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How to deal with USB pins on XL232 devices?

Postby CousinItt » Mon Nov 12, 2018 8:22 pm

Hi all,

according to the data sheet for the XL232, it has some USB pins. Are these present because it's a knobbled XU232 without a USB controller?

Is there any guidance on what to do with these pins when USB isn't (and presumably can't be) used?

Thanks
Redeye
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Postby Redeye » Tue Nov 13, 2018 10:22 pm

I've got a 3 x XL232 design where all of the USB pins are left floating. I can't honestly remember if this was what was recommended by XMOS when they reviewed the design.
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mon2
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Postby mon2 » Wed Nov 14, 2018 12:00 am

Every article read so far (5+) on the net from assorted silicon suppliers and this topic states the same as Redeye has posted, just leave the USB D+/D- pins floating. The additional question is what to do with the voltage rails for the USB PHY, etc. I would leave room for just-in-case to power such pins. Better to ask XMOS through a support ticket to clarify and post your feedback here for future readers.
Redeye
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Postby Redeye » Wed Nov 14, 2018 9:30 am

On my design I've got power to the USB supply pins. Again, I can't remember if this was what was recommended by XMOS, but the schematic was checked by them before I got the board made.
CousinItt
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Postby CousinItt » Wed Nov 14, 2018 11:39 am

Thanks mon2 and Redeye. I'll raise a ticket and post results here.
CousinItt
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Postby CousinItt » Thu Nov 22, 2018 1:03 pm

I posted a ticket. They said "post your question on the xcore support forum".

Still waiting...
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mon2
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Postby mon2 » Tue Dec 04, 2018 7:49 pm

Hi. We are reviewing a design with USB 2.0 hub controller and came across this topic of how to disable the USB port via straps.

While this may be an overkill for the XMOS CPU, it is an option to consider. Apply 0 ohm resistors to +3v3 to park the D+ and D- lines.

usb_hub_disable_port.png
(57.23 KiB) Not downloaded yet
usb_hub_disable_port.png
(57.23 KiB) Not downloaded yet
CousinItt
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Posts: 88
Joined: Wed May 31, 2017 6:55 pm

Postby CousinItt » Fri Dec 07, 2018 4:09 pm

Hi mon2 - sorry I missed your message. Thanks for the tip.

Still hoping someone from xmos might actually get around to answering this.

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