Why doesn't the serial communications work on a Smart-UPS SUA model when USB communications has been tried first?

Issue:

Connecting a USB cable to an SUA Smart-UPS disables the serial port
  
Product Line:

Smart-UPS

Environment:

All SUA models, All Serial Numbers

Cause:

Normal operation.

Resolution:
In order to regain serial communications with an SUA model Smart-UPS after USB has been used, the USB cable must be removed and the Smart-UPS must be brain deaded. To brain dead a Smart-UPS, the load must be turned off and unplugged. Next, the UPS must be turned off and unplugged. Once unplugged, push and hold the off button for 6 to 8 seconds. The sensitivity light in the back of the UPS should go out and there should be a small audible click in the unit. Serial communications should be enabled at this point and the UPS can be again plugged in and started up.