HART is a master-slave communication protocol, which means that during normal operation, each slave (field device) communication is initiated by a master communication device.
Two masters can connect to each HART loop.
The primary master is generally a distributed control system (DCS), programmable logic controller (PLC), or a personal computer (PC).
The secondary master can be a handheld terminal or another PC. Slave devices include transmitters, actuators, and controllers that respond to commands from the primary or secondary master