Can't connect Cura to my Anet A8 on OSX 10.11.6
There are a lot of problems with the CH340 chipset drivers to be found on 3D SE and various forums on the internet. To use this cheap CH340 chip that is used by a number of Arduino compatible (clone) boards to provide USB connectivity (a USB bus converter chip that converts USB bus signals to serial interface) you need to install a correct working driver. 

For Mac OS X you can try to download a working version for the OS system you are using. You can try to use this driver installer or this driver installer. Both reported to work with Mac OS.



Edit: If you are using OSX El Capitan, please read this. To  get the CH340 drivers to work you need to use the tool csrutil.


  
  Reboot and press CMD+R immediately after hearing the startup sound to boot to Recovery Mode
  Open Terminal
  Execute the following command: csrutil enable --without kext
  Reboot
  


More information is found here!