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Chapter 4

Block Reference

4-10

©

 National Instruments Corporation

Table 4-4 describes the 

Limit

 subfield values.

The block’s mode behavior is controlled with the 

MODE_BLK

 parameter. 

The 

MODE_BLK

 parameter contains four fields that allow the current mode 

of the block to be read and the desired mode for the block to be written. The 
four fields are 

Target

 mode, 

Actual

 mode, 

Permitted

 mode, and 

Normal

 mode.

The desired mode of execution for the block. An operator or process 
engineer normally writes this to put the block in the desired mode of 
operation.

Table 4-4.  Limit Values

None

The value is not limited.

Low

The value is at a lower limit. This can be caused by 
a transducer limitation or setpoint limits.

High

The value is at a high limit. This can be caused by 
a transducer limitation or setpoint limits.

Constant

The value is at a fixed value and cannot move. This 
can be caused by the block supplying the value 
being in manual mode.

Table 4-5.  Target Modes

Out of Service

Out of Service

, and optionally any other 

valid target mode

Manual

Manual

Automatic

Automatic

Cascade

Cascade

 and 

Automatic