Yokogawa YVP20S - Manual (Page 36)

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<Toc> <Ind> <5. FOUNDATION FIELDBUS OVERVIEW>
5.3 Block Modes
All blocks (function/transducer/resource) have operating modes. There are eight modes
defined in the Foundation fieldbus specification. Not all modes are supported by every
block. For example, the Discrete Input (DI) block supports just Auto, Man, and OOS. The
action of the modes are described in the following paragraphs. Transfers between modes
are managed by the function blocks in response to manual commands, in response to
changes in the modes of linked blocks, and in response to changes in the quality of the
parameters that are transmitted. Control and status options can be set to manage mode
changing behavior.
(1) Remote-Output (Rout)
The block output is being set by a Control Application running on an interface Device
through the remote-output-in parameter. The algorithm is bypassed and the remote block
controls its output directly. The algorithm must initialize so no bump is experienced when
the mode switches to auto. A remote-output-out parameter is maintained by the block to
support initialization of the control application when the block mode is not remote-output.
The setpoint may be maintained or, optionally, be initialized to the process variable value.
(2) Remote-Cascade (RCas)
The block setpoint is being set by a Control Application running on an interface device
through the remote-cascade in parameter. Based on this setpoint, the normal block
algorithm determines the primary output value. A remote-cascade out parameter is
maintained by the block to support initialization of the control application when the block
mode is not remote-cascade.
(3) Cascade (Cas)
A setpoint value supplied by another function block through the Cascade input parameter is
used by the normal block algorithm in determining the primary output value. This
connection between function blocks is defined by a link object.
(4) Automatic (Auto)
A local setpoint value is used by the normal block algorithm in determining the primary
output value. The local setpoint value may be written by an operator through an interface
device.
(5) Manual (Man)
The block output is not being calculated, although it may be limited. It is directly set by the
operator through an interface device. The algorithm must initialize so no bump is
experienced when the mode switches. The setpoint may be maintained or, optionally, be
initialized to the process variable parameter value or to the setpoint value associated with
the previous (retained) target mode.
(6) Local Override (LO)
Applies to control and output blocks that support a track input parameter. In the local
override mode, the block output is being set to track the value of the track input parameter.
The algorithm must initialize so no bump is experienced when the mode switches from LO
back to the target mode. The setpoint may be maintained or, optionally, be initialized to the
process variable parameter value.
(7) Initialization Manual (IMan)
The block output is being set in response to the back-calculation input parameter status.
When the status indicates there is no path to the final output element, then the control
blocks must initialize to provide for bumpless transfer when the condition clears. A back-
calculation out parameter is supported by all output and control class function blocks. The
setpoint may be maintained or, optionally, initialized to the process variable parameter
value.