Rosemount 848T Especificações descarregar pdf (Página 105)

Reference Manual

00809-0100-4697, Rev GA

Appendix C: FOUNDATION Fieldbus Technology

November 2014

FOUNDATION Fieldbus Technology

Figure C-4. Scheduled Data Transfer

C.5.4 Unscheduled transfers

Figure C-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.

All of the devices on the F

OUNDATION 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.

Figure C-5. Unscheduled Data Transfer

LAS = Link Active Scheduler

P = Publisher

S = Subscriber

CD = Compel Data

DT = Data Transfer Packet

P = Publisher S = Subscriber PT = Pass Token M = Message

Schedule

X, Y, Z

CD(X,A)

DT(A)

Device X

Device Y Device Z

ACDAB

PS PS P

LAS

Schedule

X, Y, Z

PT(Z)

Device X Device Y Device Z

ACDAB

PS PS P

LAS

DT(M)

1 2 ... 100 101 102 103 104 105 106 107 108 109 110 ... 135 136

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