Patent ID: 7109883

Claim:
A process variable transmitter, comprising: connections that are mateable and demateable with an accessory load; the connections including a bus contact and a common contact; a transmitter circuit having a common conductor coupled to the common contact, and having a supply conductor, and having a serial input and a serial output; a receiver circuit coupled to the serial input and coupled to the bus contact by a serial bus; a supply limiter circuit drawing a supply current from the supply conductor and providing a stored energy output; the supply limiter circuit providing a supply current limit; a recessive driver circuit drawing a drive current from the stored energy output and coupling the drive current to the serial bus, the recessive driver circuit providing a drive current limit; and a dominant driver circuit coupled between the serial output and the serial bus; the dominant driver circuit having a dominant state in which it conducts the drive current to the common conductor, and an inactive state in which the drive current is available to the accessory load.