Multi-protocol field device in process control systems

A field device 10 includes a network communication interface 23 such as an Ethernet or Profinet interface. The interface 23 may use a communication multiplexer 24 such as a transmission control protocol (TCP) multiplexer to establish one or more virtual circuits 12 and 13 over the common channel or link 11; the device further includes a plurality of communication unit circuitry 22, Pa-Pn, any or all of which can be configurable to use one of any number of different protocols, the first communication circuitry Pa having a first communication protocol such as Ethernet/IP, Profinet and the second communication circuitry Pn having a second communication protocol such as HART-IP, Foundation Fieldbus which is different from the first communication protocol. Alternatively, the field device includes only one communication unit Pb which is configurable to use different communication protocols at different times but can only use one protocol at a time. The field device has a memory 50 that stores communication protocols used to configure the single circuit Pb communication unit.