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Can I run FX3 with only USB 3.0 signals (leaving USB 2.0 signals unconnected) | Cypress Semiconductor

Can I run FX3 with only USB 3.0 signals (leaving USB 2.0 signals unconnected)

Summary: 2 Replies, Latest post by Lumpi6 on 19 Aug 2014 09:34 AM PDT
Verified Answers: 0
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piyamate's picture
1 post

My project is still in the design stage.

In the design, the FX3 device would be connected through many moving parts (robot arm). The space is very tight and minimum wiring is preferred. I was thinking about connecting two twisted pairs cables for USB 3.0 TX/RX lines and leave USB 2.0 DP/DM unconnected. Further looking into this, I found from the AN76405 EZ-USB FX3 Boot Options that FX3 only boots from USB 2.0 mode (not 3.0).

So my first question is: 
Is there any way to let me boot/load the firmware over the USB 3.0 connection ?
I found that there is a second stage bootloader called Fx3BootAppGcc. Can this firmware run in the USB 3.0 SuperSpeed mode ? If so, I could initially connect a USB 2.0 cable to my board and programme this bootloader into a flash memory (SPI/I2C). Then, everytime the FX3 boots, it runs that firmware and accepts RAM downloading from Control Center via USB 3.0 SuperSpeed mode.

If not, my alternative would be to connect only USB 2.0 part of the FX3 chip for my application. I don't mind having a lower speed. I just need the GPIF II functionality and the ARM9 processor. In that case, my second question would be:
Can I connect only USB 2.0 (DP/DM) wires to FX3 and run the ARM/GPIF with the limited bandwidth of USB 2.0 ?

kalev's picture
96 posts


Device enumerating at USB 3.0 SuperSpeed presupposes its enumerating at USB 2.0 mode first. Host switches to Superspeed mode only after retrieving device configuration descriptors in USB 2.0 mode. So, USB 2.0 must be supported, i.e. wires connected.

USB 3.0 wires can be left unconnected - this is identical to attaching device to Host USB 2.0 port.

If you do not need SuperSpeed bandwidth, then I strongly suggest to limit with USB 2.0 mode only. This communication is more reliable. Getting FX3 SuperSpeed mode working reliably is quite challenging. See for example


Lumpi6's picture
341 posts



both scenarios are possible.


Using a bootloader in I2C EEPROM or SPI Flash which can connect through USB3.0 and then give the ability to upload a application which also works with USB3.0.


Using just USB2.0 HS. This would be the easiest way as Kalev wrote in his post (no memory necessary, easier to get USB2 to run rather than USB3)




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