National Instruments NI-FBUS - Manual (Page 29)

Chapter 2 Using the NI-FBUS Configurator
NI-FBUS Configurator User Manual 2-6 ni.com
Function Block Modes
The most common operational modes for function blocks on devices are
Automatic (
Auto ), Cascade ( Cas ), Manual ( Man ), and Out Of Service
( OOS ).
• In Automatic mode, the block is running under its normal automatic
control, using a local setpoint value in the normal block algorithm to
determine the output value.
• In Cascade mode, the block is receiving its setpoint value from another
function block for use in the normal block algorithm to determine the
output value. A linkage object makes the connection between the two
blocks. The linkage object is created implicitly when you wire the
output of one function block to the input of another as described in the
Create and Edit Function Block Applications section. For example,
a PID function block receives its setpoints from an upstream block.
• In Out Of Service mode, the block is not running at all. Normally, this
mode is used during block configuration. Some devices require that the
function block be in Out Of Service mode when changing certain
parameters.
• In Manual mode, the block output is not being calculated by the normal
block algorithm. The operator writes the output of the block directly.
The MODE_BLK Parameter
The MODE_BLK parameter for a function block is the parameter that
contains information on the modes of the block. It has four fields: TARGET ,
ACTUAL , PERMITTED , and NORMAL . PERMITTED and NORMAL are defined
by the device manufacturer.
• PERMITTED contains a list of all allowable modes for that block.
• NORMAL is the mode the device manufacturer expects the block to be
in during normal operation.
• ACTUAL is the current operating mode of the function block on the
device.
• TARGET is a field that is writable by the user. Writing this field tells the
device to change to the specified mode. The device will attempt to
change the mode. If it is successful, the
ACTUAL mode changes to
reflect the TARGET mode.