@pierrot10 which model of the expansion board arte you using. Version 2 (one push button) or version 3 (two push buttons). Version 2 is more simple. If you cannot see the serial port, it is a problem of the physical connection (cable, jumpers on the board) or the OS X driver. Version 3 adds to the list of trouble sources the firmware in the PIC controller on the board. I assume that you also do not get a REPL prompt.

For who wants to try, there is a fix for this issue on the develop branch now. See my last comment in https://github.com/pycom/pymakr-atom/issues/1#issuecomment-324798001