Directional fault indication in data transmission systems - has TTL circuit to activate both indicators if fault is on incoming line

摘要

The control mode of alarm indicator display in data transmission systems is modified to allow not only the occurrence of a fault to be indicated, but also the transmission direction. Two alarm contacts; one for general fault indication and one for direction are coupled to a transistor switching stage controlled by a latch circuit. The switching stage is externally clocked by two signals. An output transistor is coupled to transistor stages controlling indicator lamps. - In the event of a fault on an incoming transmission line both lamps are activated and if the fault occurs on an outgoing line then only one lamp is illuminated.