YOKOGAWA STARDOM FCN-500, Engineering Manual

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<8. Detailed Description>
139
TI 34P02K35-02E Jun. 6, 2018-00
Scan cycle 1
Task A
Input
processing
Control/calculation processing
Output
processing
Scan cycle
Task B
Input
proces-
sing
Control/
calculation
processing
Output
proces-
sing
Input
proces-
sing
Control/
calculation
processing
Output
proces-
sing
Input
proces-
sing
Control/
calculation
processing
Output
proces-
sing
Scan cycle 2 Scan cycle 3
Logic M Logic N
Variable P ON
In the next figure, Task B copies the data of global variable P into variable Q at the
beginning of control/calculation processing and reads variable Q during control and
calculation processing. In this way, even if the value of variable P changes during
Task B’s control/calculation processing, the value read remains unchanged within
the same control cycle as the value change will only be reflected in variable Q at the
beginning of the next control/calculation processing cycle.
Logic M
Logic N
Scan cycle 1
Task A
Input
processing Control/calculation processing
Output
processing
Scan cycle
Task B
Variable P
ON
Input
processing
Control/calculation processing
Scan cycle 2
Scan cycle 3
Logic M Logic N
ON
Input
proces-
sing
Control/
calculation
processing
Output
proces-
sing
Input
proces-
sing
Control/
calculation
processing
Output
proces-
sing
Input
proces-
sing
Control/
calculation
processing
Output
proces-
sing
Variable Q
Sender task
When sending data for a BOOL-type global variable, maintain its ON or
OFF state for a duration not shorter than the recipient's scan cycle.
In the example shown in the figure below, pulse-type data of global variable P turned
on by Task A, is read by Task B, which has a different control interval at Logic M in
the latter half of Task B’s control/calculation processing.
Moreover, in compliance with the precaution described earlier for a recipient task,
data of variable P is copied at the beginning of Task B into variable Q, which is read
during control/calculation processing.
The value of variable P is OFF when it is copied into variable Q by Task B. When
variable P is subsequently turned on during the Task A’s control interval, this change
is not propagated immediately to variable Q so Task B may fail to receive ON states
of variable P.