What does the UD bit in the GPIO control register actually do?

Question: What does the UD bit in the GPIO control register actually do? What does the circuit look like for the ESD protection circuit?

 

Answer:

There is an error in the datasheet regarding the UD bit in the GPIO Control Register (0xC006). This bit actually controls internal diagnostics used by Cypress Semiconductor during test and characterization. This bit should be reserved and not used in customer applications. This is true for both EZ-Host and EZ-OTG.