ABSTRACT
It is a bidirectional, half duplex, interoperable digital process control and automation fieldbus protocol. Foundation fieldbus is a two-level architecture consisting of lower-level H1and upper-level high speed Ethernet (HSE) and supports both scheduled and unscheduled communication. It is based on seven layer open system interconnection (OSI) protocol but uses only physical, data link, and application layers. Application layer is subdivided into fieldbus access sublayer (FAS) and fieldbus message specification (FMS). It also has an additional layer—layer 8, called the “user layer.” It has function block, transducer block, and resource block. Operating speed at H1 level is 31.25 kbps.
Manchester coding is used for communication with field devices being supplied with 9 V to 32 V DC. Maximum number of field devices in a segment is 32. Field devices are classified into link master (LM) range, BASIC range, default range, and temporary range.
Data link layer’s most important job is medium access control (MAC) and a link active scheduler (LAS) does this job.
An application clock synchronizes field devices based on macro cycle and elementary cycle.
Redundancy can be incorporated in Foundation Fieldbus at host level, device level, media level and network level to ensure availability of resources in times of breakdown.
