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MPC5748G USB Dependency on UART

Question asked by Steve Lyon on Feb 22, 2017
Latest reply on Mar 9, 2017 by Steve Lyon


We are experiencing a weird issue on our MPC5748G where the USB is unreliable without a valid level on LIN1RX.

We are using the Green Hills RTOS and the Microchip USB83340 transceiver on ULPI0, connected as a USB device to a host CPU running Linux.

We have LIN1 on PC6/7 going to a header that we use as a debug terminal with the FTDI smart cable.

If the FTDI cable is unconnected, our USB connection will consistently drop.

When the FTDI cable is connected or I add a 100k pull up on LIN1RX, then the connection is fine.

It is also interesting that when our debug nexus probe is connected which pulls high all of the MDO signals on ports L and M, then that also fixes USB.


Is there any reason why the debug UART or nexus probe would have any affect on the USB?