Rockwell Automation PLC-5 Fieldbus Solutions for Integrated Architecture User Manual - Manual (Page 22)

Publication 1757-UM006A-EN-P - May 2002
1-8 The Fieldbus Communication Model
About Modes of Operation
Every Function block includes a mode parameter with configured
permitted modes. This structured parameter is composed of the actual
mode, the target mode, the permitted mode, and the normal mode.
The normal mode is the desired operating mode. The actual mode
reflects the mode used during block execution. The target mode may
be set and monitored through the mode parameter. The permitted
mode defines the allowable target mode settings. The following table
provides a summary of the available modes of operation and their
effect on operation.
Table 1.C Modes of Operation
Mode Abbreviation Operation Effect
Out of Service OOS The block is not being evaluated. The output is maintained at the last value, an assigned failsafe
value -last value or configured failsafe value. Set Point is maintained at last value.
Initialization
Manual IMan The block output is being set in response to the back-calculation input parameter status. When
status is no path to the final output element, control blocks must initialize to provide for bumpless
transfer, when the condition clears. The Set Point may be maintained or initialized to the Process
Variable parameter value.
Local Override LO Applies to control and output blocks that support a track input parameter. Also, manufacturers may
provide a local lockout switch on the device to enable the Local Override mode. The block output is
being set to track the value of the track input parameter. The algorithm must initialize to avoid a
bump, when the mode switches back to the target mode. The Set Point may be maintained or
initialized to the Process Variable parameter value.
Manual Man The block is not being calculated, although it may be limited. The operator directly sets it through an
interface device. The algorithm must initialize to avoid a bump, when the mode switches. The Set
Point may be maintained, initialized to the Process Variable parameter value, or initialized to the Set
Point value associated with the previous (retained) target mode.
Automatic Auto The block's normal algorithm uses a local Set Point value to determine the primary output. An
operator may set the value of the Set Point through an interface device.
Cascade Cas The block's normal algorithm uses a Set Point value fed through the Cascade input parameter from
another block to determine the primary output value.
Remote
Cascade RCas The block's Set Point is being set by a Control Application running on an interface device through
the remote-cascade in parameter. The block's normal algorithm uses this Set Point to determine the
primary output value. The block maintains a remote-cascade out parameter to support initialization
of the control application, when the block mode is not remote-cascade.
Remote-Out ROut The block's output is being set by a Control Application running on an interface device through the
remote-output in parameter. The algorithm must initialize to avoid a bump, when the mode
switches. The block maintains a remote-output out parameter to support initialization of the Control
Application, when the block mode is not remote-output. The Set Point may be maintained or
initialized to the Process Variable parameter value.