FC 97 - Redundant Digital Input

The redundant digital input function code selects and transfers a pair of redundant boolean signals. An external logic select input <S3> controls the transfer. The output value is equal to the input value selected with <S3>.

 

Function code 97 monitors the action of the two inputs <S1> and <S2>. Output quality is bad if the quality of the selected input is bad or if there is a difference between the two inputs when both have good quality. To test the quality of the signal, include a function code 31 in the configuration. The quality of the point cannot be used as an input to any other type of block. However, the output value can be used as an input to other blocks.  Refer to Appendix H, for a definition of point quality.  

 

Outputs:

Blk

Type

Description

N

B

Output N = <S1> if <S3> = 0

Output N = <S2> if <S3> = 1

 

 

Specifications:

Spec

Tune

Default

Type

Range

Description

S1

N

0

I

Note 1

Block address of first input

S2

N

0

I

Note 1

Block address of second input

S3

N

0

I

Note 1

Block address of select input; 0 = <S1>, 1 = <S2>

 

 

97.1 Applications

 

Function code 97 depends on external logic to select and output one of two redundant boolean inputs. The configuration shown in Figure Figure 97-1 illustrates the output of a function code 98 controlling the selection. If the active module in the function code 98 changes from module one to module two, then the active input in the function code 97 block switches from input one to input two. Configuring the blocks so that inputs one and two correspond to modules one and two insures that if one module goes bad, the input from the other module will automatically be read.