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TUSB4020BI: The TUSB4020 and our USB nullmodem cable are detected by linux, but there is no USB communication with the Terminal

Part Number: TUSB4020BI
Other Parts Discussed in Thread: AM3505

Hello, Texas team.


We are using an embedded AM3505 processor's USB0 port to control the TUSB4020. 

We use a USB nullmodem cable to allow console access from a terminal program (e.g Putty or Teraterm).

This console port is connected to port USB_DP_DN1 / USB_DM_DN1 of the TUSB4020.

This has worked satisfactorily for almost all of our PCBs.

We have two boards that exhibit a fault:


After power-up, we can see both the TUSB4020 and the null model cable detected by linux as expected:-


Bus 003 Device 003: ID 0403:6001

Bus 003 Device 002: ID 0451:8027

BUT - There is no communication with the terminal program.


Given that all the inputs/voltages  of a "faulty" board are the same as a working board, is there some other parameter that would stop the USB_D(P)(M)_DN1 port from working?

OR - is it likely that the TUSB device has been damaged?