Inverted High Speed FX3 pins on Cypress demoBoard. Why?

[Anonymous]

 Hi all,

   

I have bought the FX3 Development Kit device board and i noticed that SS_RX_P and SS_RX_M are inverted on the demo board.

   

On the Micro-Type B USB3.0 connector the pin 9 corresponds to SS_RX_M and the pin 10 corresponds to to SS_RX_P. when the wires come out of the connector, we see that SS_RX_M and SS_RX_P are inverted before to go to the U1 chip. This is located on the sheet 9/14 in the attached file.

   

The FX3 communication on the demo board occurs good. I have also developped a new board with FX3 and the two pins are not inverted. I encounter some trouble with the communication. I am getting errors at every transaction. I think that errors are linked to inverted FX3 pins and also to layout pcb because the two High Speed pins don't go directly to chip but go through vias.

   

What do you think about it ?

   

Thanks in advance for your help

   

Kind Regards

[Anonymous · Accepted solution]

Hi,

   

USB3.0 allows checking the polarity through hardware handshake and reverse the polarity if needed ( To make the life of PCB designers easy by making the routing of the USB3.0 lines easier). That is the reason behind the swap.

   

Coming to High-speed lines,

   

Avoid routing D+ and D– through vias; vias introduce impedance mismatch. Where vias are necessary(e.g., using mini-B connector) keep them small (25-mil pad, 10-mil hole) and keep the D+ and D– traces on the same layers.

       

Thanks,

   

Sai Krishna.

[Anonymous]

 Does the USB2.0 lines on FX allow to swap?

       

The document says "The  polarity  can  be  swapped  on  the  USB  3.0 differential  pairs."  I'm confusing if the D+/D- pairs belongs to the USB3.0 differential pairs.

[Anonymous]

Hi,

   

No, we can not swap USB2.0 lines. It is valid only for USB 3.0 differential data lines.

   

Thanks,

   

sai krishna.