Question about designing with CYUSB3304

[Anonymous]

Dear sir:

   

When I design a USB HUB with CYUSB3304, I read the document 001-94150, in the chapter "Downstream (DS) Connectors", the DS1_RXP pin is connected to USB StdA_SSRX- pin, while the DS1_RXM pin is connected to USB StdA_SSRX+ pin, I think the correct connection should be:

   

DS1_RXP-----------USB StdA_SSRX+

   

DS1_RXM-----------USB StdA_SSRX-

   

Is the connection in the document right?

   

And can the DS_DM/DP/RXM/RXP/TXM/TXP pins be left floating when the DS port isn't in use?

[Anonymous]

Hi,

   

Yes, it is correct. The lane polarity swapping/inversion is possible only for SS_RX pair i.e., SS_RXP and SS_RXN can be connected interchangeably for layout routing convenience to ensure that USB traces do not cross each other. The polarity inversion will be taken care by the TSEQ training sequence during link training. For more details on how the receiver detects this inversion, please refer 'section 6.4.2 in USB3.0/3.1 specification'.

   

 Yes, the unused pins of D+/-, SS_TX+/-, SS_RX+/-have to be left floating.

   

Regards,

   

Anil

[Anonymous]

Thank you very much!

   

You mean SS_TXP and SS_TXN can not be swapped?

[Anonymous]

Yes, you are right.

   

Regards,

   

Anil

[Anonymous]

Thank you!

   

But could you please explain why?

[Anonymous · Accepted solution]

The lane polarity inversion is taken care by the receiver through TSEQ training sequence during link training as mentioned earlier.

   

The TX pair of one IC is connected to the RX pair of the device at the other end if two ICs or devices are interconnected. So, in this scenario the receiver of other IC will take care of the polarity inversion on the TX pair enabling lane inversion on both TX and RX pairs.

   

If the Hub is having downstream removable ports, the receiver of the Hub will take care of the lane inversion on RX pair and some devices' receivers might not capable of implementing automatic polarity detection. In this case, swapping the TX pair may result in the unsuccessful enumeration of the device on the downstream port of the Hub.

   

This is the reason why we don't recommend the polarity inversion on TX pairs on downstream ports.

   

Regards,

   

Anil 

[Anonymous]

I see.

   

Thank you for your explanation!