Abstract: A prior art crossbar switching system provides a test frame connector which may be seized by a marker for the purpose of causing a trouble data record to be made (e.g., by a trouble recorder card perforator). All markers compete for normal seizure of the connector by means of the usual connector seizure circuit arrangement of preference relays and connector relays whereby normal marker seizure attempts are recognized and served so that only one normal seizure at a time is permitted. A new interface circuit is provided so that a computer can effect a special seizure of an idleconnector and so that no normal seizure attempt can be recognized by the seizure circuit while the special seizure situation prevails; however, the interface can detect a normal seizure attempt which occurs at any time while the special seizure is in the process of being effected.