Configuration Manual Owner manual

Publication 1757-PM002A-EN-E - June 2006
Basic Function Blocks 3-15
VCRs: 6 total; 3 Publisher, 3 Subscriber
QUU and QUB VCR Classes
The QUU and QUB VCR classes are defined as user triggered. During the
unscheduled portion of Foundation Fieldbus communications, these are the
class of communication that occur when the available time is sensed by the
devices. QUU and QUB communications take place when the Link Active
Scheduler passes the token to the devices, allowing them to communicate.
The QUU class can be defined as the reporting link with function blocks.
Specifically, the QUU VCR is used to report contained parameter values in
function blocks such as alarms and change of state. HMI information such as
alarm conditions and device calibration data uses this type of configuration
with an existing strategy.
The QUB class can be defined as the command link with function blocks.
More specifically, the QUB VCR is used to change contained parameter values
in function blocks such as MODE or Set Point. HMI interaction via a
faceplate or a configuration tool uses this type of communication with an
existing strategy.
Since the QUU and QUB VCR use the asynchronous portion of the
macrocycle, enough time must be made available. The focus during
configuration is to make the macrocycle as small as possible to allow function
block execution to occur quickly. Minimizing the asynchronous portion of the
macrocycle will adversely affect QUU and QUB VCR from taking place, since
that time must also be used for housekeeping activities such as probe nodes.
If there is an expectation of increased communication with devices, either
from a control or HMI monitoring standpoint, then the macrocycle should be
increased. This is to be done with the understanding that the function block
cycle time will be increased as a consequence. Therefore, judicious choice of
macrocycle times must be exercised to allow effective QUU and QUB
communications.
FB 1
LGX
Device 1