Possible Carrier errata? USB device mode.

I'm trying to get my picozed to operate in USB device mode, and apart from the massive struggle with Petalinux kernel configuration, I'm starting to wonder if the hardware is not part of the problem as well.

According to page 74 of the USB phy datasheet:
(http://ww1.microchip.com/downloads/en/DeviceDoc/3320.pdf)

The Vbus pin of the phy needs to be connected (with appropriate series resistance and bypass capacitance) to the +5V power coming from the host.

The jumpers on the carrier board allow for appropriate configuration in terms of Rvbus and Cvbus mentioned above, but diode D5 on the carrier board is preventing the phy from seeing the +5V from the host. I suspect that this will prevent it from enabling its pull-up speed-identification resistor on D+ which is what tells the host that a device is connected.

Can anybody confirm for me that their PicoZed+Carrier board is capable of operating in device mode? and if so can you share your linux image and/or kernel configuration options?

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0 drozwood90 over 10 years ago

trjeppsdl,

The Symbol on the schematic might be a little confusing, but this is not a DIODE in the traditional sense. It is a voltage protection circuit. The diode is there as a voltage sense / protection gate.

The voltage from pin 1 to pin 3 is free to flow (0.16ohm typical R). However, if the voltage from pins 1 to 3 becomes larger than 5.45V (min) - 5.75V (max) the Zener component will "short" to ground up to it's MAX rating (~10A until the part is damaged). This ensures that if there is a transient or voltage spike (typically tested using a human body model http://en.wikipedia.org/wiki/Human-body_model) the sensitive 5V circuits are not damaged. This can be typical depending on the environment when plugging and unplugging cables. If you look at the end of the USB cables, you can even see that the outside pins (power and ground) are longer. They are designed that way so as to engage the protection circuit before the data lines are even connected.

If you check the datasheet (http://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Specification+Or+Standard%7FSCD26730%7FF%7Fpdf%7FEnglish%7FENG_SS_SCD26730_F.pdf%7FRF1489-000) for the part, you can see what I mean on bottom of page 2.

From the sounds of your issue, I agree with Gary that you probably do not have the CPEN pin configured properly.

--Dan
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0 drozwood90 over 10 years ago

trjeppsdl,

The Symbol on the schematic might be a little confusing, but this is not a DIODE in the traditional sense. It is a voltage protection circuit. The diode is there as a voltage sense / protection gate.

The voltage from pin 1 to pin 3 is free to flow (0.16ohm typical R). However, if the voltage from pins 1 to 3 becomes larger than 5.45V (min) - 5.75V (max) the Zener component will "short" to ground up to it's MAX rating (~10A until the part is damaged). This ensures that if there is a transient or voltage spike (typically tested using a human body model http://en.wikipedia.org/wiki/Human-body_model) the sensitive 5V circuits are not damaged. This can be typical depending on the environment when plugging and unplugging cables. If you look at the end of the USB cables, you can even see that the outside pins (power and ground) are longer. They are designed that way so as to engage the protection circuit before the data lines are even connected.

If you check the datasheet (http://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Specification+Or+Standard%7FSCD26730%7FF%7Fpdf%7FEnglish%7FENG_SS_SCD26730_F.pdf%7FRF1489-000) for the part, you can see what I mean on bottom of page 2.

From the sounds of your issue, I agree with Gary that you probably do not have the CPEN pin configured properly.

--Dan
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