fieldbus is an all digital, serial, bi-directional communication protocol that interconnects devices such as actuators, sensors, discrete devices, and controllers in the field. It is a Local Area Network (LAN) for instruments that enables basic control and I/O to be moved to the field devices.
In the DeltaV system, the H1 fieldbus card connects to the fieldbus segment and interfaces with fieldbus devices. The H1 card connects to any vacant slot in an I/O Interface Carrier. The H1 card has two ports and each port can connect to one fieldbus segment. Up to 16 devices are supported for each segment.
FOUNDATION Fieldbus is a specific fieldbus technology developed and supported by Emerson and the other members of the independent fieldbus Foundation. FOUNDATION Fieldbus technology uses Device Descriptions and function blocks to enable intelligent field devices to execute control functions traditionally performed by a distributed control system.
H1 fieldbus technology is modeled on the Open Systems Interconnect (OSI) model and consists of three parts:
Physical Layer - receives messages from the Communication Layer (Stack) and converts them into signals on the fieldbus segment; receives signals on the fieldbus segment and converts them into messages
Communication Layer - (Communication Stack made up of the Data Link Layer, fieldbus Access Sublayer, and fieldbus Message Specification). The Data Link Layer controls transmission of messages on the fieldbus segment.
User Application Layer - DeltaV applications, such as Control Studio and Explorer
The User Application Layer is not defined by the OSI model. FOUNDATION Fieldbus specifies a User Application Model that Fisher-Rosemount used to develop DeltaV software applications.