For the same UNO and USB cable, Arduino IDE 1.7.11 shows the serial communication ports and uploads work fine, but with a new install of Arduino IDE 1.8.1, the Tools->Port is greyed out.
My Apple Mac OS is 10.11.6.
I have tried connecting, disconnecting the USB cable, and closing and opening the IDE. The Port continues to be greyed out for IDE 1.8.1.
Thanks in advance for any suggestions.