Function Block Scheduling; Network Management - Fisher FIELDVUE DVC6200f Instruction Manual

F fieldbus Communication
OUNDATION
July 2013
D Report Distribution: This type of communication is used to broadcast and multicast event and trend reports.
D Client/Server: This type of communication is used for request/ response exchanges between pairs of devices, such
as a set point change. Like Report Distribution reporting, the transfers are queued, unscheduled, and prioritized.
Queued means the messages are sent and received in the order submitted for transmission, according to their
priority, without overwriting previous messages.

Function Block Scheduling

Figure D‐6 shows an example of a link schedule. A single iteration of the link‐wide schedule is called the macrocycle.
When the system is configured and the function blocks are linked, a master link‐wide schedule is created for the LAS.
Each device maintains its portion of the link‐wide schedule, known as the Function Block Schedule. The Function Block
Schedule indicates when the function blocks for the device are to be executed. The scheduled execution time for each
function block is represented as an offset from the beginning of the macrocycle start time.
Figure D‐6. Example Link Schedule Showing Scheduled and Unscheduled Communication
Device 1 AI
Scheduled
Communication
Unscheduled
Communication
Device 2
0
B2715‐1
To support synchronization of schedules, periodically Link Scheduling (LS) time is distributed. The beginning of the
macrocycle represents a common starting time for all Function Block schedules on a link and for the LAS link‐wide
schedule. This permits function block executions and their corresponding data transfers to be synchronized in time.

Network Management

Information for setting up network communications, including Virtual Communication Relationships (VCRs), host
timer recommendations, and other network parameters, can be found in the capabilities file (.cff) available from the
website www.FIELDVUE.com or from the Fieldbus Foundation website.
296
Macrocycle Start Time
Offset from macrocycle
start time = 0 for AI Execution
Offset from macrocycle
start time = 20 for AI
Communication
Offset from macrocycle
start time = 30 for AI
Execution
PID AO
Offset from macrocycle
start time = 50 for AO
Communication
20 40 60 80 100
Macrocycle
Start of Next Macrocycle
Sequence Repeats
AI
PID AO
120 20 40 60 80
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