Emerson FIELDVUE DVC6200f, Instruction Manual

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F
OUNDATION
Fieldbus Communication
November 2010 271
B2715-1 / IL
Sequence Repeats
AI AI
AO AO PID PID
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
Device 1
Scheduled
Communication
Unscheduled
Communication
Device 2
Macrocycle
0 20 40 60 80 100 120 20 40 60 80 100 120
Offset from macrocycle
start time = 50 for AO
Communication
Start of Next Macrocycle
Figure D-6. Example Link Schedule Showing Scheduled and Unscheduled Communication
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.
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.
D