Specifications

FOUNDATION Fieldbus Overview
22 Connection to FOUNDATION Fieldbus IM/265/7/9/ADD/FF-EN_01
In the Fig. 8 is represented the macro
cycle of the above loop. The LAS functionality inside the
controller provides to handle the loop, and the macro-cycle is the temporary representation of
how, function blocks and communications, are scheduled. From the instant 0 to 20 the AIFB is
executed, in the period from 20 to 30 the LAS provide to schedule the AIFB output. The
Pressure Transmitter provides to publish the pressure value, the PIDFB subscribes this value.
Then the PIDFB is executed from the instant 30 to 40 and at the end, the PIDFB output is
scheduled and goes in input to the AOFB without communications because the two Function
blocks reside inside the same device.
The unscheduled communications are always active unless during the period between 20 - 30
when the pressure value is published on the bus.
The LAS functionality handling the control loops, is also available inside the models
265 / 267 / 269 FF Revision 1. Referring to the Fig. 9, whenever failure of the controller occurs,
and th
e LAS
1
stops its execution, the 2600T previously set as back-up LAS
2
take care of the
loop maintaining alive the Fieldbus executing the same macro cycle that was active before of
the controller failure.
Important
When more than 1 field device is configured as LAS Backup, the one with lower Node Address
has high priority for assuming the control when the Primary LAS fails.
M00511
Controller
Control System-
Netw ork
+
?
x
?
x
H1
Te rmination
LAS
1
LASLASLAS
2
IEC 1158-2 with 21.25 Kbits/s
Pressure Tx Valve P re ssure Tx
Fig. 9: Back-up LAS diagram
Further and detailed descriptions about the FOUNDATION Fieldbus concepts refers to the
“Technical Overview'” document FD-043 available on the Fieldbus Foundation website
(www.fieldbus.org
).