Different conditions of a module are indicated by means of at least one
visual indicator element, for instance in the form of a light emitting
diode, mounted visibly on the module. Pressing a repair key initiates a
repair condition, in which the actions and control procedures necessary
for taking the faulty module out of service are carried out, and also
causes a newly inserted module in a module frame to be automatically
recognized, prompts a test function and causes the new module to be
automatically put into service upon passing a test procedure.
