$ASYNC_AXIS = 'B000000' or 0 means none are asynchronous
$ASYNC_AXIS = 'B000001' or 1 means E1 only is asynchronous, other external axes are synced
$ASYNC_AXIS = 'B000010' or 2 means E2 only is async, other external axes are synced
$ASYNC_AXIS = 'B010011' or 19 means E1, E2 and E5 are async, other extern axes are synced with robot
from last example it is obvious why binary format is preferred in this case.