<9. Advanced Engineering >
● Connecting Functions When Using EN Terminal
To use the EN terminal to start or stop the execution of logic connecting multiple
functions, you must connect the ENO terminal of the upstream function to the EN
terminal of the downstream function.
In the logic shown below, calculation D= (A+B)*C is performed only while EN01 is
TRUE.
In the above figure, the ENO terminal of the upstream ADD logic is connected to the
EN terminal of the downstream MUL logic.
The ENO terminal of a function is TRUE when the function is executed so if its EN
terminal is TRUE, its ENO terminal is also TRUE.
Conversely, if its EN terminal is FALSE, its ENO terminal is also FALSE.
Therefore, the EN terminal of the MUL logic is TRUE only when the EN terminal of
the ADD logic is true so the above calculation logic is executed only when EN01 of
the ADD logic is TRUE.
● Incorrect Connection of EN Terminals
The figure below shows an example of an incorrect connection whereby the ENO
terminal of the ADD logic is not connected to the EN terminal of the MUL logic.
In this case, the ADD logic is stopped or started depending on the value of variable
EN01, but the MUL logic is executed in every scan cycle.
In the above example, the calculation result of the ADD logic is connected to and
passed to the terminal of the MUL logic. When EN01 is FALSE, the output result of
the ADD logic is an indefinite value (not guaranteed to be the calculated value in the
preceding task control cycle), which is then used in the calculation of the MUL logic
to produce an indefinite calculation result.
If the upstream ENO terminal is connected to the downstream EN terminal as shown
in the example of correct connection, when EN01 is FALSE, the MUL logic is not
executed so even if the calculation result of the ADD logic is indefinite, there is no
problem.
EN01
ADD
MUL
B
C
D
A
EN
EN01
ADD
MUL
B
C
D
A
EN
(* Example of Correct Connection *)
(* Example of Incorrect Connection *)
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