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FX2LP fails to enumerate | Cypress Semiconductor

FX2LP fails to enumerate

Summary: 2 Replies, Latest post by Gayathri on 13 Sep 2012 12:25 AM PDT
Verified Answers: 0
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prophet36's picture
13 posts

I have three identical FX2LP boards, one of which works fine, the other two fail to enumerate. Has anyone got any hints for things I can try (hardware and/or software) to discover what's up?

The working board enumerates like this:

The non-working boards are detected as high-speed devices:

...but fail to respond to the host's descriptor requests:

The hardware is pretty minimal:

1) 56-pin SSOP CY68013A (1st bad board) and CY68014A (2nd bad board)

2) D+, D- & GND connected to USB

3) Reset circuit: 22nF capacitor charged through 100K resistor

4) Clock circuit: 24MHz crystal and a pair of 22pF capacitros

5) Two 22nF decoupling capacitors

6) External 3.3V PSU

7) Everything else unconnected (for now)

prophet36's picture
13 posts

Never mind, I fixed it.


I noticed a design fault in my schematic - the SDA line has a removable link to allow the FX2 to be isolated from its EEPROM. Unfortunately, the pull-up on the SDA line is on the EEPROM side, not on the FX2 side as it should be. So the SDA line on the FX2 was floating. I soldered in the link and all is well. I guess since SDA was left floating the startup behaviour is undefined; it just happened to work on one board and not on the others.

gaya's picture
Cypress Employee
578 posts



Thank you for posting the fix. It might be useful for others with similar issues.




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