Unscheduled Transfers - Fisher FIELDVUE DVC6200f Instruction Manual

Instruction Manual
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Figure D‐4. Scheduled Data Transfer
Host System
LAS
Schedule
X
Y
Z
CD (X, A)
LAS=Link Active Scheduler
P=Publisher
S=Subscriber
CD=Compel Data
DT=Data Transfer Packet
B2713‐1

Unscheduled Transfers

Figure D‐5 diagrams an unscheduled transfer. Unscheduled transfers are used for things like user‐initiated changes,
including set point changes, mode changes, tuning changes, and upload/download. Unscheduled transfers use either
report distribution or client/server type of reporting for transferring data.
Figure D‐5. Unscheduled Data Transfer
Host System
LAS
Schedule
X
Y
Z
LAS=Link Active Scheduler
P=Publisher
S=Subscriber
PT=Pass Token
M=Message
B2714‐1
All of the devices on the fieldbus are given a chance to send unscheduled messages between transmissions of
scheduled data. The LAS grants permission to a device to use the fieldbus by issuing a pass token (PT) message to the
device. When the device receives the PT, it is allowed to send messages until it has finished or until the "maximum
token hold time" has expired, whichever is the shorter time. The message may be sent to a single destination or to
multiple destinations.
DT(A)
A
B
P S
Device X
PT (Z)
B
A
M
S
P
Device X
F
A
C D
P S P
Device Y Device Z
C A D
P S P
Device Y Device Z
fieldbus Communication
OUNDATION
A
S
A
M
S
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