Error handling at the FB level
The individual FBs' error outputs refer to errors that have occurred within the scope of command issuing to an FB instance, not to the errors of the axis. This is why incorrect command issuing sets only the commanded FB to an error state. The incorrect command itself is not even issued by the FB and so the axis (FBSD) is not even set to an error state. Therefore, other FB instances located on the same axis do not notice anything.