Patent ID: 8344880

Claim:
A field device of automation technology, which is fed via a two-wire line or via an energy source of limited energy reserve associated with the field device, comprising: a hardwired communication interface having at least one communication channel; a functional unit associated with the hardwired communication interface which is embodied in such a manner, that it performs sending and/or receiving of digital communication signals via said hardwired communication interface, said functional unit, for the purpose of energy saving, is turned on only in active, operating phases, while it is switched off in inactive, resting phases; and a detection circuit, which detects a communication signal applied to said hardwired communication interface and automatically activates said functional unit, wherein: said detection circuit includes a high resistance coupled comparator circuit, which monitors the communication channel for electrical current, and/or voltage, modulations, which indicate a communication signal; and said high resistance coupled comparator circuit includes a low energy, or low power, comparator with open-drain output, which, in the case of occurrence of a communication signal, produces a positive-negative edge, which switches a microprocessor associated with said communication circuit active, so that the operational phase is activated.