Specifications

FOUNDATION Fieldbus Overview
IM/265/7/9/ADD/FF-EN_01 Connection to FOUNDATION Fieldbus 21
Approvals
7 FOUNDATION Fieldbus Overview
In the Fig. 7, is represented how the Function Blocks inside the FF devices connected on the
bus, can be linked together in order to achieve a simple control loop. After the loop has been
designed, the LAS Master device located in the Controller or, as back up, in the slave device
itself, starts the scheduling of the Function Block executions and of the publisher / subscriber
communications in a deterministic way.
M00509
AI
OUT
PID
IN
AO
OUTOUT IN
Pressure
Valve
Fig. 7: Simple Single Loop configuration example
In the example of Fig. 7, the Pressure Transmitter implementing the AIFB publish the pressure
value, then the PID
FB implemented in the valve, subscribe this value from the bus in order to
be used as input for the PIDFB. In the same way the exchange of values between the PIDFB
and the AOFB occurs but without communications on the bus, because the two Blocks are
inside the same device.
M00510
0 20 40 60 80 100 120 20 40 60 80 100 120
DL Offset = 0 for
AI execution
DL Offset = 20 for
AI communication
PID AO PID AO
DL Offset = 30 for
PID execution
DL Offset = 50 for
AO execution
Device 1
Macrocycle
LAS
Macrocycle
Unscheduled
communication
permitted
Device 1
Macrocycle
Absolute Link Schedule Start Time
Sequence Repeats
LAS Schedule duration LAS Schedule duration
HD
RE
V
AI AI
Fig. 8: Macro-cycle example